用逗号隔开的第一二句，第二句long fraught with controversy and still held to be a pseudoscience by some 修饰第一句global difference in intelligence is a sensitive topic 或者具体一点修饰a sensitive topic ，作定语。可以改成定语从句。
global difference in intelligence is a sensitive topic which has been long fraught with controversy and still been held to be a ps...
首先第一个问题，“ long fraught with controversy and still held to be a pseudoscience by some”是补充说明，修饰前面的整个句子，而不是只修饰这个sensitive topic。至于most clever这个问题，clever的最高级有两种，一是cleverest，二是most clev...
