开门见山说明来意就行。
Dear xxx:
Many thanks for the insightful comments and suggestions of the referees. I have made corresponding revision according to their advice. Words in blue are the changes I have made in the text（为了便于审稿人重审，一般把修改过的地方用醒目颜色标出）。
按照审稿人的意见逐条进行了修改
The following is the answers and revisions I have made in response to the reviewers' questions and suggestions on an item by item basis.
1.
2.
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