El contrato de alquiler de auto incluye el deducible.

Because contrato is a specific countable noun here, and Spanish normally uses the definite article el with it: el contrato = the contract.

In Spanish, articles are often used more regularly than in English. So even where English might sound slightly more flexible, Spanish usually prefers the article in a full sentence like this.

It is a chain of noun + de + noun structures:

• contrato de alquiler = rental contract / contract for rental
• alquiler de auto = car rental

So the whole phrase contrato de alquiler de auto means something like:

• car rental contract
• literally, contract of rental of car

Spanish often links nouns this way with de, where English might use one noun directly in front of another.

Because auto is being used in a general/classifying sense, not to mean a specific car.

• alquiler de auto = car rental / rental of a car
• alquiler del auto = rental of the car

So de auto means the type of rental, while del auto would refer to one particular car already known in context.

Yes. This is a regional vocabulary choice.

In Latin America, different countries prefer different words for car:

• auto — common and widely understood
• carro — common in many countries
• coche — more common in Spain, but also used in some Latin American areas

So alquiler de auto is perfectly natural in much of Latin America, but depending on the country you might also hear:

• alquiler de carro
• alquiler de coche
• renta de auto

Alquiler is a noun meaning rental or renting.

It comes from the verb alquilar, which means to rent.

For example:

• alquilar un auto = to rent a car
• el alquiler de auto = the car rental

So in this sentence, alquiler is not a verb. It is a noun inside the larger noun phrase contrato de alquiler de auto.

Incluye is the third-person singular present indicative form of incluir (to include).

It matches the subject el contrato, which is singular:

• El contrato incluye... = The contract includes...

Other forms would be:

• incluyo = I include
• incluyes = you include
• incluyen = they include

Because el deducible is a direct object, and it is a thing, not a person.

Spanish uses the personal a mainly before specific human beings (and sometimes pets or personified beings), not before ordinary things.

So:

• incluye el deducible = correct
• incluye a el deducible = incorrect

Yes. Here deducible is being used as a noun, meaning deductible in the insurance/coverage sense.

Even though deducible can also function as an adjective in other contexts, in this sentence it is clearly a noun, so it takes the article:

• el deducible = the deductible

This is common in insurance and rental contexts.

Not exactly. Nouns ending in -e can be masculine or feminine, so the ending alone does not decide it.

You simply learn the gender with the word:

• el deducible

So in this usage, it is masculine.

Usually, el deducible sounds more natural here because it refers to the deductible amount/coverage condition associated with the contract.

Without the article, incluye deducible, it sounds less complete and less standard in this kind of sentence. In formal or neutral Spanish, incluye el deducible is the better choice.

Yes. A few natural alternatives are:

• El contrato de alquiler de auto incluye el deducible.
• El deducible está incluido en el contrato de alquiler de auto.
• El contrato de alquiler del auto incluye el deducible. — but this usually means the rental contract for the specific car

A very common variation in many places would also be:

• El contrato de renta de auto incluye el deducible.

The original sentence is correct and natural, especially in a neutral Latin American style.

Because Spanish often builds noun phrases with de, where English frequently stacks nouns together.

Compare:

• English: car rental contract
• Spanish: contrato de alquiler de auto

This is one of the most common differences between English and Spanish. English often puts nouns directly next to each other; Spanish usually connects them with de.

You could say things like:

• El contrato de alquiler de auto incluye el deducible del seguro.
• El contrato incluye la cobertura con deducible.
• El contrato cubre el deducible.

Each one shifts the nuance a bit:

• incluye el deducible = the deductible is included
• incluye el deducible del seguro = specifically the insurance deductible
• cubre el deducible = the contract covers/pays for the deductible

So the best version depends on the exact context.