一般by都是用于被动句 I was hurt by the knife. 或者表示一种方式 I go to school by bike. 或者表示在。。。之前 I have to send this letter by tomorrow.(明天之前)一般by都是用于被动句 I was hurt by the knife. 或者表示一种方式 I go to school by bike. 或者表示在。。。之前 I have to send this letter by tomorrow.(明天之前)