Li Hua's parents hold different opinions on whether they should have _______ child．（ ）
A．anotherB．otherC．othersD．the other
We will fail the exam____we study hard．
That's why we are trying our best to prepare for the exam．（ ）
A．untilB．whenC．unlessD．how
How time flies！We should show love for our parents and make them ______how much they mean to us．（ ）
A．to knowB．knowingC．knewD．know
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