Davalac krvi bira dobrovoljno davanje krvi.

Davalac means giver or donor. In this context, davalac krvi is the standard formal way to say blood donor.

It comes from the verb davati = to give. Serbian often forms nouns for people from verbs, so davalac is literally someone who gives.

Because Serbian uses the genitive case after nouns like davalac and davanje to express of blood.

So:

• krv = blood
• krvi = of blood

That is why you get:

• davalac krvi = donor of blood
• davanje krvi = giving/donation of blood

English usually uses noun-noun combinations like blood donor, but Serbian often uses a noun + genitive structure instead.

Because it belongs to two different noun phrases:

• davalac krvi = blood donor
• davanje krvi = blood donation / giving blood

Each phrase needs its own krvi. In English, this may feel repetitive, but in Serbian it is normal and clear.

If you removed the second krvi, dobrovoljno davanje would just mean voluntary giving/donation, without specifying what is being donated.

Here is the basic breakdown:

• Davalac — nominative singular
  It is the subject of the sentence.

• krvi — genitive singular
  It depends on davalac: donor of blood.

• bira — verb, 3rd person singular present

• dobrovoljno davanje — accusative singular
  This is the direct object of bira.

• krvi — again genitive singular
  It depends on davanje: donation of blood.

A useful detail: davanje is a neuter noun, and its nominative and accusative forms are the same, so you do not see a form change here.

In this sentence, dobrovoljno is best understood as an adjective agreeing with davanje.

Why? Because davanje is a neuter singular noun, and the adjective dobrovoljan becomes:

• masculine: dobrovoljan
• feminine: dobrovoljna
• neuter: dobrovoljno

So:

• dobrovoljno davanje krvi = voluntary blood donation

If it were an adverb modifying the verb, it would mean something like chooses voluntarily, which is less likely here.

Compare:

• dobrovoljno davanje krvi = voluntary blood donation
• dobrovoljno daje krv = gives blood voluntarily

Davanje is a verbal noun formed from davati = to give.

It means giving, and in context it can also mean donation. Serbian often uses these verbal nouns in formal, medical, legal, or administrative language.

So davanje krvi is literally giving of blood, but in natural English it is often rendered as blood donation.

Bira is the 3rd person singular present tense of birati = to choose / select.

So bira can mean:

• chooses
• is choosing, depending on context

Here it is a regular present-tense form:

• ja biram = I choose
• ti biraš = you choose
• on/ona bira = he/she chooses

Because Serbian does not have articles like English a/an/the.

So Davalac krvi can mean:

• a blood donor
• the blood donor
• blood donors in a generic sense, depending on context

You have to get definiteness from the situation, word order, or the broader text.

Yes, it is grammatical, but it sounds formal and somewhat institutional because it uses nouns like davalac and davanje instead of a more everyday verbal style.

That kind of wording is common in official, medical, or campaign language.

A more conversational sentence would often use a verb more directly, but the given sentence is perfectly understandable and normal in a formal register.

Not in this sentence as written. Here it naturally goes with davanje:

• dobrovoljno davanje krvi = voluntary blood donation

If you wanted to describe the person as a voluntary blood donor, Serbian would usually say:

• dobrovoljni davalac krvi

So the form helps you see what is being modified:

• dobrovoljni → masculine singular, matching davalac
• dobrovoljno → neuter singular, matching davanje

This is a straightforward subject + verb + object order:

• Davalac krvi = subject
• bira = verb
• dobrovoljno davanje krvi = object

Serbian word order is more flexible than English, but this order is neutral and easy to understand.

If you changed the order, the sentence might still be grammatical, but the emphasis could shift. The given version is the most straightforward one for presenting the idea clearly.