英语语法选择题（说明原因）
1.Sheep _____genetically engineered.
A.have being B.are been C.are being
2."We _____that this is a major concern for phone users,"said the spokesman.
A.learnt B.had learnt C.have learnt
3.I can do that job.I_____one of those machines before.They____the same printer software at my old company.
A.used B.have used