几个初中英语语法题求助（1）-Each of students ,working hard at his or her

几个初中英语语法题求助
（1）-Each of students ,working hard at his or her lessons,___ to go to university.
-So do I.
A.hope B.hopes c.hoping D.hoped
[答案是B,为什么不是C呢?]
(2)I,___your friend,will help you when in need.
A.that am B.which am C.who is D.who am
[……这题我就知道B不对其它完全无法辨别= =这真是给初三学生的题吗噗]
（3）You ___that mistake,you were too careless.
A.should not have made
B.should not make
C.ought not have make
D.must not have make
[……为什么B不对?
看着这题我纠结了……!
非限定性定语从句是什么…… 第二题答案是C