They offered courses _________ students know the importance of protecting the Huanghe River．（ ）
A．helpB．helpedC．helpsD．to help
______ the light，please．This is a room with enough natural light．（ ）
A．Turn offB．Turn onC．Turn down
The singer________ while still at school（ ）
A．has discoveredB．was discovered
C．discovered
Thomas is the________ player in the basketball team but he is the best．（ ）
A．shorterB．shortC．shortest
The man________ called yesterday wants to buy the house．（ ）
A．whoB．whatC．which
I ordered a hamburger and salad．________ hamburger was nice but the salad was not delicious．（ ）
A．AnB．TheC．A