21. Many lifestyle patterns do such __________ great harm to health that they actually speed up __________ weakening of the human body .
A. a ; / B. / ; the C. a ; the D. / ; /
22. --- Why on earth didn’t you answer the phone ?
--- I’m terribly sorry , but the doorbell __________ , too .
A. is ringing B. rang C. was ringing D. was about to ring
