从句可以与非谓语动词互换。
If you check your composition carefully, you can at least avoid some spelling mistakes.
=Checking your composition carefully, you can at least avoid some spelling mistakes.
=Check your composition carefully, and you can at least avoid some spelling mistakes.
Having checked 表示检查的动作在先,避免拼写的错误在后,语意错。应该的检查的时候就可以避免拼写错误,所以用 checking,不用having checked 。
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