The correct answers would be era(ser) and gustaba(gustar)
Cuando mi prima rosa era pequeña, a ella le gustaba mucho el chocolate.
When my cousin rosa was little, she liked chocolate very much.
This a would be the correct answer since it is in imperfect form
Era= was
Gustaba= liked
This means that this was using past tense which includes the imperfect.
Hope this helps! :3