英文句子分析：I agree with the speaker's assertion that ...

英文句子分析：I agree with the speaker's assertion that ...
I agree with the speaker's assertion that self-knowledge is elusive for tracing the meaning of selfhood proves to be an extremely difficult task.
这是新东方 GMAT 写作句型模仿里面的一个例句.proves 的主语是哪个?还是说这个句子本身有问题?