有关于英语语法的选择题

有关于英语语法的选择题
答案已给出,我是想知道解题思路
1)Is the radio bothering you?
it certainly is.I'd like it _C_off.
A.turning B.to turn C.turned D.turns
2)As the saying goes,you _A_take a horse to the water,but you can't make it drink.
A.may B.need C.must D.should
3)If you _B_in a speaship high above the earth,where there is no air to scatter the sunlight,you would find the sky pitch-black.
A.riding B.rode C.will ride D.would ride
4)The audience stared open-mouthed as the acrobat walked on the steel wire_C_high above the ground.
A.being fixed B.has fixed C.fixed D.having fixed
5)The workers on the construction site downed tools,demanding that they _D_medical care and social security insurance.
A.provide for B.provided with
C.should provide with D.be provided with