Right answer:
b. pidiendo
This is a sentence given in the imperfect. This tense is used to talk about past actions, conditions, or events that occurred regularly or frequently or that were in progress in a moment in the past. The verb used here is the irregular verb estar whose conjugation for the third person plural in the imperfect is estaban. Therefore:
Los jóvenes estaban pidiendo ayuda para toda la comunidad translates into:
The young people were asking for help for the whole community.
