Answer :
A present participle is a verb that ends with ing signaling a continuous action, therefore in this sentence the correct choice would be 1. We are filling garbage bags with trash from the school playground.
The present participle is a participle that ends in -ing. It is used to talk about something that you are doing right now. Therefore, the correct present particple for the regular verb fill would be are filling (1).
The sentence should read, "We are filling the garbage bags with trash from the school playground."