It seems that his health is improving.---Yes.It is

问题补充：

It seems that his health is improving.---Yes.It is ten years

答案：

C,it is +time+since+句子这个句型.他不抽烟已经十年了.

看起来他的身体在好转.--是的,他已经十年不抽烟了.

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======以下答案可供参考======

供参考答案1:

B after,didn smoke

第一句的意思是：看起来他的健康在改善。

第二句的意思表示肯定：是的，他不吸烟已经有十年了。那么他不吸烟的时间起算为他不吸烟之后，所以用after，原因是：didn‘t smoked。