求高手指导几道英语选择题...关于名词部分的

求高手指导几道英语选择题...关于名词部分的
We should look up to him as a shinning example of ____ to duty.
A devotion B privilege C responsibility D burden
但是我不知道为什么,我觉得C也可以吖...（意思我都知道,但是不知道原因,总觉得怪怪的）
AIDS control and prevention is a ____ to China as well as the whole world.
A surprise B challenge C reaction D threat
可是我觉得D更好吖...想不通吖...
This is an old photo of my mother when she had ___ ,and now she has ____.
A short hair:grey hairs
B short hairs :grey hair
C short hair:grey hair
D short hairs:grey hairs
可是我选的是B,根本就是反的,到底hair 的用法是什么样的啊...犯迷糊了...
Would y0u be so kind as to give me a ___?I'm too tired to walk any further.
I'm sorry,but the car is too crowded.
A place B drive Cseat D lift
可是我记得D似乎也有搭便车的用法吖...哪位大侠可以指导一下咯...