We are now in senior three. I think it’s time we ______ more efforts for the college-entrance exams.
. By the year 2020 scientists _____ a lot of research on AIDS.
_____ is commonly believed that the play was written by Shakespeare.
He made a promise____he would achieve the success that his parents were looking forward to.
After a knock at the door, the children heard his mother’s voice him.
If we can our present difficulties, then everything should be all right?