Seventy percent of the workers here--from the countryside

Seventy percent of the workers here__from the countryside
A.is B.are C.comes D.has come16.I,who __your friend,will try my best to help you with your English.a.am B.is C.are D.be20.Can you tell me the name of the factory __you visied last week?A.what B.where C./ D.when21.The most important thing __we should pay attention to is the firs thing__I have said.A.which ;that B.that;which C.which;which D.that;that29.He told us _he had done.A.that all B.all that C.all which D.what all33.I have no idea what__while I was asleep.（happen没被动.所以..）A.happened B.had happened C.was happened D.has happened