21. David Cameron was elected _____ Prime Minister to lead Britain to _____new time.
A. /; a B, the; a C a； the D. a； /
22. I have received an offer from an American university, but I am still hesitating _______ I should accept it.
A. how B. why C. whether D. that
23．Temperatures _______quite dramatically at night in mountains, so put on some warm clothes before going out.
A. are dropped B. drop C. are being dropped D. have dropped
