We use the present progressive, also called the present continuous tense, when talking about actions that are happening now. This tense is often formed with the verb estar plus the present participle. In this way, Spanish present participles end in <em>ndo, </em>that is equivalent to the English ending <em>ing. </em>So estamos is the conjugation of the verb estar for the first person plural (nosotros) in the simple present and bebiendo (drinking) comes from the verb beber (to drink). Accordingly:
Entiendo is the correct answer because "entender," the original form of the verb, is a stem changer, e--ie, and the "yo" form in present tense ends with -o.
