第一节 单项填空（共15小题；每小题1分，满分15分）
21. Our bad living habits will destroy the earth. Only by changing ______ we live ______save the earth.
A. that, can we B. what, we can C. how, can we D. where, can we
22. Mr. Brown has three children, one of whom is a child of six, ____ twins of twelve.
A. another B. other C. the others D. others
