Sure, here are the sentences filled in with suitable relative pronouns or adverbs:

1. Barbara works for a company **that** makes bridges.
2. The book is about a girl **who** runs away from home.
3. She is the girl **who** was disliked by her step-mother.
4. An English man in America is always the one **whom** everybody wants to talk to.
5. A mystery is something **that** cannot be explained.
6. I never like people **who** are never on time.
7. We can't understand **why** he is always the one **whom** we have to wait for.
8. Bill Clinton is the man **whom** everyone knows.
9. What happened to the picture **that** was stolen 3 months ago?
10. What was the name of the horse **that** won the race?