by yourself的用法和樣例：
例句
- How long were you by yourself in the classroom?
你獨自一人在教室里多長時間了? - Are you sure you did this exercise by yourself?
這個練習真是你自己做的嗎? - Since you are already of age now, you should solve the problems by yourself.
你已經成年了，這些問題要自己解決。 - You can't go mountain climbing by yourself.
你不能自己去登山。 - I believe that you can work out this problem by yourself.
我相信你自己能做出這道題的。
