--I tried many times,but I still failed in the experiment.

题目

--I tried many times,but I still failed in the experiment.
--Don’t be discourage d． ____ and the problem will be settle ．
A． Making a little effort B． There being a little effort
C． If you make a bit effort D． A bit more effort
选D ,A为什么不行?解释选项ABCD谢谢

答案

…… and …….
and的前后各作为一句完整的话,and表示后文是前文的结果.
AB是状语从句,不能独立存在,C是if从句后面不能有and,D有省略,原句是You make a bit more effort...