-I'd like to invite you to my birthday party on Friday evening .
-Thank you,but ___I'll have time,I'm not sure at the moment.
A if Bwhether Cwhat Dwhich （为什么要选B,不能选A,A和B有什么区别）
2.Is Science Museum open to the public yet?
Yes,It ___for almost half an hour.
A was open B has opened C has been open D has been opened(为什么要选C?）