英语单选,选D,请问A为什么不行?

即使A选项换成rewards也不对.
解决本题的关键不在于get/gain的问题,而在于rewards&award的区别：
rewards：
a)something good that happens or that you receive because of something you have done;
b) money that you receive for working
award:
a)a prize or reward that is given to someone who has achieved something.
b)an amount of money that the goverment or another organization gives to someone so that they are able to do something.
建议：当你遇到有些词容易混淆时,可以查阅英文词典或者双解词典,认真领会英文的解释,这样理解的要比单纯看汉语意思更准确.

固定搭配