The engineers____a new computer in our classroom the whole yesterday morning，so we had our classes in the school hall．（ ）
A．were fixingB．fixed
C．have fixedD．are fixing
I shouted to you at the gate，but you didn't hear me．
Really？I____a telephone call to my mother．（ ）
A．makeB．was makingC．madeD．have made
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