It was not until December 25 ________ we finally heard from him.
A. which
B. that
C. when
D. then
Don't ________ other people's problems and make them your own.
A. get involved in
B. is involved in
C. be involved in
D. ge involved on
He didn't go to the World Park because he ___________ there twice.
A. has been
B. had been
C. has gone
D. had gone
The harder you work, ______ grades you will get.
A. better
B. the better
C. he more good
D. good