I did not see a post about this question, I incorrectly selected (B) without fully understanding the stimulus. Did not bother to read the stimulus properly, was being lazy and it backfired. (B) is wrong because not only is it not the Main Conclusion, but it actually goes against what the stimulus is...

The stimulus says nothing about complex which is why I thought (D) was wrong. It says poor writers express mundane ideas with complex language, but mundane means boring/dull, it is not to my understanding that mundane means "COMPLEX". You could have a complex idea which is mundane, they me...