Dintre apă și lapte, eu aleg apa.

Dintre means out of or from among. It is very common when someone is choosing one thing from a group of options.

• dintre apă și lapte = out of water and milk
• între apă și lapte = between water and milk

Both can appear with choices, but dintre highlights selection more clearly. In this sentence, it fits the idea of picking one option from two.

After dintre or între, Romanian normally links the two items with și.

So:

• dintre apă și lapte = out of water and milk

The idea of choice already comes from aleg = I choose.
You would use sau in a different structure, for example:

• Apă sau lapte? = Water or milk?

But after dintre, și is the normal choice.

The phrase Dintre apă și lapte has been moved to the front of the sentence for emphasis, so it is separated with a comma.

It works like an introductory phrase in English:

• As for water and milk, I choose water.
• Out of water and milk, I choose water.

The comma helps show a pause and makes the structure clearer in writing.

Yes. Aleg already tells you the subject is I.

Romanian often drops subject pronouns when they are not needed:

• Aleg apa. = I choose water.

Adding eu gives emphasis, contrast, or clarity:

• eu aleg apa = I choose water / I’m the one who chooses water

So eu is optional here, but it adds stress.

This is because Romanian puts the definite article at the end of the noun.

• apă = water
• apa = the water

For many feminine nouns ending in -ă, the definite form changes like this:

• casă → casa
• masă → masa
• apă → apa

In this sentence, the first apă is just the name of one option in the list. The second apa is the specific option the speaker chooses.

Because in dintre apă și lapte, the two nouns are being listed as options in a general way, so the bare forms are natural:

• apă
• lapte

Then in the second part, the speaker identifies the chosen item specifically:

• aleg apa

So only the selected item is made definite here. If the speaker chose milk instead, they would say:

• Dintre apă și lapte, eu aleg laptele.

Romanian word order is fairly flexible, but different orders sound more or less natural depending on what you want to emphasize.

Very natural:

• Dintre apă și lapte, eu aleg apa.
• Dintre apă și lapte, aleg apa.
• Eu aleg apa.

The version with dintre apă și lapte at the front emphasizes the set of options first.
The version without eu is less emphatic.
So the sentence you were given is grammatical and natural, especially if the speaker is contrasting their choice with someone else’s.

Ă is a very common Romanian vowel. It sounds like the a in English sofa or about.

So:

• apă is roughly AH-puh
• the first a is a clear a
• the final ă is a short, relaxed uh

The stress is on the first syllable:

• Á-pă

Aleg comes from the verb a alege = to choose.

Here, aleg is:

• present tense
• 1st person singular
• meaning I choose

Some present-tense forms are:

• eu aleg = I choose
• tu alegi = you choose
• el/ea alege = he/she chooses
• noi alegem = we choose
• voi alegeți = you all choose
• ei/ele aleg = they choose

So the core statement aleg apa simply means I choose the water / I choose water in this context.