【C17】A．must have beenB．may have beenC．could have beenD．should have been

This is the first time the students ______ to Hyde Park.A、have beenB、have been goneC、hav

SIX MUST－HAVE COMPUTER SKILLS FOR STUDENTSDo you have the computer skills you should hav

They are sweating all over. They ______ in the field.A．may beB．must have been workingC．cou

I have no idea who stole his wallet. It _____anyone.A. must have beenB. should have been

It______last night. But I am not sure.A．may rainB．might rainedC．must rainD．may have rained

【C7】A．has beenB．have beenC．had beenD．to have been