"What do you drink?"
Translation:तुम क्या पीते हो?
In more colloquial Hindi that may be the case. My understanding is this sentence, including तुम, would not be unnatural if spoken aloud. For the sake of learning, it is simpler to stick to fewer constructions and introduce dropping the subject later.
Because of the verb conjugation, तुम can be inferred, and thus can be dropped. It's similar to how Spanish doesn't necessarily require the pronoun due to the verb conjugation, e.g. "Que bebes?"
I don't think so. In Hindi, rarely the pronouns are dropped, usually only when being present at the same place as the person the sentence is for and pointing towards them.
On submitting क्या पीती हो, I was marked wrong and the correct sentence was given as आप क्या पीती हो. It's a glaring error to say आप ... हो, and I have reported the sentence accordingly.
Its a difference of saying "is" for singular and plural.. the "haen" is for plural, "ho" is for singular..