since it is already midinght,we-------

since it is already midinght,we_______
A)had better leaving
B)ought to have leave
C)should take our leave
D)might as well leave
请说明选择的原因,为什么不能选B和C
2)i wonder if he_____us,and i think if he______us we'll be able to complete the task ahead of time
A)helps,help
B)will help,helps
C)will help,will help
D)helps,will help
请说明选择的原因,为什么不能选别的答案,并帮我翻译全句