问题描述：
i regret to tell you this,but...
i regret to tell you this,but i broke the window.
为什么要用but.
还有一个.
it's hard work climbing mountains.
it's hard work后加doing
i regret to tell you this,but i broke the window.
为什么要用but.
还有一个.
it's hard work climbing mountains.
it's hard work后加doing
问题解答：
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