-I’d like to invite you to my birthday party on Friday eveni

-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?）

第一题：在介词后,只能用whether
区别：（1）.whether可与or not连用,而if不可以；
（2）.在句首时用whether,而不用if；
（3）.在介词后用whether,而不用if；
(4).可以与动词不定式连用 He can’t decide whether to visit her or not.他决定不出是否去看她.(5).表示“如果”时用if,而不用whether.
第二题：强调持续的一个状态.