1.All flights-----because of the storm,they decided to take

1.All flights_____because of the storm,they decided to take the train.A.having been cancelled B.have been cancelled 为什么选A?不能选B?2._____that there are no objection,we will begin with item three on the agenda.A.If B.Provided为什么选B,不能选A?3._______is the center of our planetary system was a difficult concept to grasp in the Middle Ages.A.That the sun and not the earth B.It is the sun and not the earth为什么选A?不能选B?4.I______to go to their party but I was not invited.A.should have liked B.would like第4题为什么选A？不能选B？