SAT二道语法题,

题目

SAT二道语法题,
1.After [many years] of training,some artists are so skilled [in reacting at] any stimulus that they [can quickly] retaliate if attacked.
[in reacting at] 错,求这个词组的正确用法/固定搭配,
2.A a person [need not] purchase tools.(我简化成了题干)
这里[need not]没错,请问为什么不是"needs"

答案

第一题 in reacting at 并不是一个固定搭配,前面的词组是 be skilled in sth or doing sth,而react在此是不及物动词,其用法如下：不及物动词 vi.
1.作出反应,反应[(+to)]
How did she react to the news?
她对这个消息反应如何?
2.影响,起作用[(+on/upon)]
The two react upon each other.
这两者互相影响.
3.抗拒,反抗[(+against)]
Children tend to react against their parents by going against their wishes.
孩子们通常以违背父母的意愿来反抗他们.
4.起反作用,回过来起作用[(+on/upon)]
Unkindness often reacts on the unkind person.
恶人往往有恶报.
5.【化】起化学作用;【物】反应[(+with/on)]
How do acids react on metals?
酸对金属会起怎样的化学反应?
An acid can react with a base to form a salt.
酸和碱反应会产生盐.
此句是第一种用法,所以应用reacting to
第二题涉及到need的用法,它既可用做实义动词,也可用做情态动词,在此句中,因为其后加了not,故是情态动词,没有第三人称单数,也就不可加“s”.