11.such...as,the same...as固定搭配的时候都用as引导定语从句.例如：I want to use the same dictionary as you used yasterday.
考查介词＋which的用法.she buys the ring with the money.with“用”,她用钱买了戒指,money用which来代指,with不能丢掉.
18.考查介词＋which的用法.she was travelling on the train,on which.
19.冬天是一年中白天变短夜晚变长的时候.先行词为time,在定语从句中缺少时间状语,所以用when,选择C.