His mother _____ teacher.
The doctor did _______ he could ________ the little child.
Miss Chen can show you around _______ mountain, because she has ______ good knowledge of it.
The athletes competed ________ each other for gold medals in the Olympic Games.
All his free time is ______ by volunteer work, but he feels it meaningful.
Bill Gates is so _____ that he has given away most of his money to the poor.