by不能改成什麼，它做介詞和副詞用。
例如by加交通工具，表示乘什麼，by boat，by subway，by train等。
例句：They went to school by train yesterday afternoon.
還有短語by the way，by here，by somebody.
例句：By the way，Where is Jenny Brown?
例句：Chinese is spoken by many people.
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