Our city is cleaner than it______be．（ ）
A．is used toB．used toC．uses toD．is used
All the students _____ know cheating in the exam is not allowed．（ ）
A．needB．mayC．mustD．can
Two disabled men from Hebei Province （one is blind and the other has no arms） have spent over ten years____ trees together．（ ）
A．plantB．plantsC．plantingD．planted
We must protect plants because they are friends of____．（ ）
A．weB．usC．ourD．ours
Prime Minister Li Keqiang arrived in Shiyan____May 23nd，2016．（ ）
A．atB．onC．inD．from
As we all know，Wudang Mountain is the ____of Shiyan．（ ）
A．proudB．prideC．progressD．purpose