El contrato de alquiler de auto incluye el depósito de garantía.

Because the subject is El contrato, which is singular.

• El contrato = the contract
• incluye = includes

So the verb has to match that singular subject:

• El contrato ... incluye ...
• not El contrato ... incluyen ...

If the subject were plural, then you would use incluyen:

• Los contratos de alquiler de auto incluyen el depósito de garantía.

In this sentence, de is connecting nouns, similar to of in English, though in natural English we often translate it more smoothly.

You have:

• contrato de alquiler = contract of rental / rental contract
• alquiler de auto = rental of a car / car rental
• depósito de garantía = deposit of guarantee / security deposit

So de is building noun phrases.

A good way to see the structure is:

• El contrato
  
  • de alquiler
  • de auto

That means something like:

• the car-rental contract

And:

• el depósito
  
  • de garantía

means:

• the security deposit

Spanish often uses noun + de + noun where English might prefer an adjective or a compound noun.

Because de auto is talking about the type or category of contract, not about one specific car.

• de auto = related to car rental in general
• del auto = of the car, referring to a specific car already known

So:

• contrato de alquiler de auto = car rental contract
• contrato del auto = the car’s contract / the contract of the car

Using del here would change the meaning.

Remember:

• de + el = del
• but only when you really mean of the

Since this sentence is talking generically, de auto is the right idea.

It can be, but it depends on the country.

In Latin America, you may also hear:

• alquiler de auto
• renta de auto
• alquiler de carro
• renta de carro
• arrendamiento de vehículos (more formal/legal)

A few regional notes:

• auto is common in some countries, especially in the Southern Cone.
• carro is very common in much of Latin America.
• coche is more associated with Spain, though it is also used in some places.

So the sentence is understandable, but in some regions another version might sound more natural, such as:

• El contrato de renta de carro incluye el depósito de garantía.

All three can mean car, but usage varies by region.

• auto: common in places like Argentina, Uruguay, and others
• carro: very common in many Latin American countries
• coche: very common in Spain; less common in much of Latin America for this meaning

So for a learner, the important thing is:

• They may all be understood,
• but one may sound more natural than another depending on the country.

If your focus is Latin American Spanish, carro is often a safe everyday option in many areas, though not everywhere.

Because both nouns are being presented as specific nouns in the sentence:

• El contrato = the contract
• el depósito = the deposit

Spanish uses definite articles very often, sometimes more often than English does.

Here, the speaker is referring to:

1. a specific contract being discussed, and
2. a specific deposit associated with that contract.

So the articles are completely natural.

Also notice the gender:

• contrato is masculine → el contrato
• depósito is masculine → el depósito

This is another noun + de + noun structure.

• depósito = deposit
• garantía = guarantee

Together, depósito de garantía means security deposit.

Spanish often expresses these ideas literally as:

• deposit of guarantee

but in natural English we usually say:

• security deposit

So this is a very common structural difference between English and Spanish.

Other similar examples:

• tarjeta de crédito = credit card
• sala de espera = waiting room
• cinturón de seguridad = seat belt

Sometimes yes, if the context is already clear.

For example, if everyone is already talking about renting a car or an apartment, a speaker might shorten it to:

• incluye el depósito

But depósito de garantía is clearer and more precise, especially in formal, legal, or customer-service language.

So:

• depósito = possible in context
• depósito de garantía = more explicit

It can definitely be phrased differently.

Other possible versions include:

• contrato de alquiler de autos
• contrato de renta de auto
• contrato para alquilar un auto
• contrato de arrendamiento de vehículo (more formal)

A small note: in many contexts, de autos may sound more natural than de auto because businesses or services are often described in the plural:

• alquiler de autos
• venta de autos
• seguro de autos

But the singular version can still appear, especially as a generic label.

Yes, but the original sentence is very natural.

Original:

• El contrato de alquiler de auto incluye el depósito de garantía.

Possible alternatives:

• El depósito de garantía está incluido en el contrato de alquiler de auto.
• El contrato de alquiler de auto ya incluye el depósito de garantía.

The first version changes the focus to the deposit.
The original focuses on the contract and what it includes.

So the word order is not random; it helps show what the speaker wants to emphasize.

Because Spanish normally uses de instead of an English-style possessive structure for these kinds of relationships.

English often builds noun phrases like:

• car rental contract
• security deposit

Spanish usually prefers:

• contrato de alquiler de auto
• depósito de garantía

So instead of stacking nouns together the way English does, Spanish more often links them with de.

That is one reason Spanish noun phrases can look longer than English ones.

It sounds neutral to somewhat formal.

Words like:

• contrato
• alquiler
• depósito de garantía

are very normal in business, customer-service, and legal contexts.

In casual conversation, a person might say something simpler, depending on the country:

• El alquiler del carro incluye el depósito.
• La renta del auto ya incluye el depósito.

So the original sentence sounds appropriate for a contract, website, rental policy, or customer information.

A useful trick is to find the noun that the verb agrees with.

In this sentence:

• incluye is singular
• so ask: what singular noun is doing the action?

That noun is contrato.

Everything after it describes what kind of contract it is:

• de alquiler
• de auto

So the core structure is:

• El contrato incluye el depósito.

Then Spanish adds more detail:

• El contrato de alquiler de auto incluye el depósito de garantía.

This is a very useful reading strategy for long Spanish noun phrases.