as did------强调某个动作, 解释为：也。
例句：Tom,as did his father 25 years ago, works very hard at college.== Tom works hard at college, like his father who worked hard, too, 25 years ago.so as ------强调目的 + 动词原形。解释为：为了 例句：Tom works hard so as to be a top student in his class.
