Though this question is very difficult,if you ________ trying you will find the right answer.
Either the boy or his sister must have dinner here.
He had decided to give it up , but on____ second thoughts he decided to try___ third time.
stop fooling, boys and girls, and he .
.As is known to all,____ tiger is in____ danger of dying out.
.—Is there anyone who is gong the Great Wall? _______