A riposte is a quick and clever reply that is often made in answer to criticism of some kind.
If you are despondent, you are extremely unhappy because you are in an unpleasant situation that you do not think will improve.
If you are responsible for something, you are the cause of it and so can be blamed for it.
When you respond to something that someone does or says, you react or reply to it.
Differentiated vocabulary for your students is just a click away.