21. Was it because of the heavy snowstorm in Europe ________ the flight had to be put off？
A. which B. so C. why D. that
22 . ----- I called at your house at about 7 o’clock yesterday evening, but you weren’t in.
----- I _____ a film in the cinema.
A. saw B. had seen C. see D. was seeing
23. -----Guess what! I’ve passed my oral English test and got A.
----- congratulations. You ____ practiced a lot.
A. must have B. should have C. must D. should
