Its correct the way it is,what you can do if process of elimination to see which one sounds correct.
The clause <em>when we can rest </em>is a subordinate/dependent clause, meaning that it cannot stand on its own - it has to be a part of a larger, independent clause, as is the case here.
Answer:
Either Birds or trees
Explanation:
A noun is a person, place, or thing. Thing could either be the bird or the nest and place is the tree. Whichever is an actual option on your test or quiz.