Choose the appropriate variant. Be quiet! The baby ....

The correct answer is: is sleeping. Because the sentence 'Be quiet!' indicates that the action is happening now, at the moment of speaking. Therefore, we need to use the Present Continuous tense, which is formed with 'is/am/are + verb-ing'. In this case, since the subject is 'the baby' (singular), we use 'is' and the verb 'sleep' becomes 'sleeping'. So the complete sentence is: Be quiet! The baby is sleeping. (Тихо! Ребенок спит.)