By the time he arrived in Beijing, we _______ there for two days.
A. will have stayed B. stay C. have been staying D. had stayed
The professor could hardly find sufficient grounds________ his arguments in favor of the new theory.
A. on which to base B. which to base on C. to base on D. to be based on
Along with the email was my brother’s promise ______ I came first in the competition, he would buy me an MP4.
A. what B. that C. that if D. whether
"We can't go out in this weather," said Bob, ________ out of the window.
A. looking B. to look C. looked D. having looked
Scientists are convinced _______the positive effect of laughter ______ physical and mental health.
A. of ; at B. by ; in C. of ; on D. on ; at
Many of them turned a deaf ear to his advice, ________ they knew it to be valuable.
A. as if B. now that C. even though D. so that
