as与 which 的区别位置不同;as可放在主句后,主句前或主句中间;which只能放在主句后,as起连接作用,表达说话人的观点、看法并指出主同内容的根据或出处,意为“正如,正像”which 相当于并列问,可以用and this 来代替,意为“这一点”。注意:as常用于下列结构:as we know,as is known to all,as we all can see,as has been said before/above, as might be excepted,as is often the case 一股不能用which代替as.