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1·The letter served him as a bookmarker.

他将那封信用作书签。

2·Put a bookmarker into the book so that I can know where you have read.

书里面放上书签，我好知道你读到哪儿了。

书签

1·Put a bookmarker into the book so that I can know where you have read.

书里面放上书签，我好知道你读到哪儿了。