帮忙看看下边的英语选择题选什么?说出原因

帮忙看看下边的英语选择题选什么?说出原因
21.You ________ help me if you don't have time.I can do the job myself.
[A] aren't able to [B] don't have to [C] aren't going to [D] mustn't
22.Next August,Bob and Sue _________ for 10 years.
[A] are married [B] have been married
[C] will have been married [D] will marry
23.The sun gives off light and warmth,_________ is very important to the living things on the earth.
[A] that [B] which [C] what [D] where
24.Would you please wait for me _________ few minutes?
[A] more [B] some [C] another [D] other
25.It _________ hard when I left the house.
[A] rains [B_) is raining [C] rained [D] was raining
26.After a long discussion,they at last ________ a conclusion that the experiment should be continued.
[A] made [B] found [C] discovered [Dj drew
27.The stars are _________ when there is no moon.
[A] the brighter [B] more bright [C] brightest [D] brighter.
28.-Do you mind if Tom rides in your car?
-_________.I ' II be glad to take anybody but Tom.
[A] Certainly not [B] No,I do [C] Not at all [D] Yes,I do
29.His grandfather ________ for fifteen years.
[A] died [B] was dead [C] has been dead [D] has died
30.The light is still on.They _________ to switch it off.
[A] may forget [B] should have forgotten
[C] must have forgotten [D] can't have forgotten