请教OG里几道有关"as"的题

第十版OG中的91题：As did many self-taught artists, X did not begin to paint until she was ...       

 为什么这里的as不对呀，是哪里不对称了？请教高人~

还有，第136题，Although X is not fatal , it is so debilitating as to become an economical drai  on many developing   countries. "so as to"的运用我觉得没有问题，为什么必须改成"so that"？糊涂了呀，哪位前辈指点一下，还两周就上战场了！

刚查了老帖子，明白了

下次一定贴上题目，多谢