As nobody here knows what is wrong with the machine, we          send for an engineer to handle the problem．

Brain, like muscles, also needs some kind of exercise and nutrition. The more you use your brain in the right direction, the more you ________ enhance your ability.

--Who’s the man over there?Is it Mr Black?----It _____be him.He’s much taller.

I __________use a clock to wake me up because at six o'clock each morning the train comes by my house. 

 ---Are you pleased with the result of the math exam?  ---Not at all. I can’t have ______ one.