I would say the correct answer is girls had laughed a little nervously.
Based on this clause, we can deduce something about their personality, and that is that they are happy kids who want to laugh all the time but they are not allowed to. The other options are either direct characterization or not characterization at all.
you didnt post the passage
Being organized
Reviewing notes and rewriting frequently if necessary.
Asking questions if you do not understand even a little thing in the topic.
