21. Your room is in ______ mess! Go and put them in ______order.
A. / ; an B. a; / C. a; an D. /; /
22.Scientists are convinced ______the positive effect of laughter ______physical and mental health.
A. of; at B. by; in C. of; on D. on; at
23.Have you got any ______ to make?
A. impressions B. comments C. reactions D. opinions
