要选择这个答案的原因

要选择这个答案的原因
最好把为什么选这个答案的原因讲一下,选项的区别,
3.Will you stay for lunch?
Sorry,______.My brother is coming to see me.
A.I mustn’t B.I can’t C.I needn’t D.I won’t
10.It was so cold that the travelers had the fire ______ all the night.
A.burning B.to burn C.burn D.burnt
13.I will give ______ students ______ minutes for them to finish their exercise
A.the other; other five B.the other; another five
C.other; five more D.other; more five
15.The family ______ at the lunch table when someone came to tell them what had happened at ______.
A.were sitting; Mr Brown B.were sitting; Mr Brown’s
C.was sitting; Mr Brown D.was sitting; Mr Brown’s
(family的单复数情况讲一下）
18.Has Jack finished his homework yet?
I’ve no idea,But he ______ it the whole afternoon.
A.would do B.was doing C.did D.had done