Respuesta :
I believe that C is your answer, that is, the sentence has two adjective phrases.
Over time, this acidic groundwater eventually eats away at the rock, leaving an underground chamber, or cave.
Take the verb "to eat away", it is transitive, so it selects two complements. The NP subject "this acidic groundwater" and the PP "at the rock". The head of the NP is premodified by the qualitative adjective "acidic". That is one of the AdjPs (adjective phrases).
What's more, the VP (verb phrase) of the subordinate clause (leaving an underground chamber, or cave), "to leave" is a transitive verb so it also takes two complements: an implicit subject and a D.O (direct object). The NP "an underground chamber, or cave" is the direct object and its head is premodified by the adjective "underground". Therefore, the statement indicating that the sentence has two adjective phrases is the one that is true.