几个英语选择题,可以告诉我选它们的理由吗?

几个英语选择题,可以告诉我选它们的理由吗?
We were flying ______the clouds and saw the blue sky.（C）
A.overB.onC.aboveD.up
Which subject are you best_____?(C)
----Physics.
A.onB.inC.at
Can youtell the difference______the three photos _______ color?( A )
A.between,inB.between,of
C.of,betweenD.of,in
between不是两者之间吗?怎么可以用between呢?
疑惑……