.She is the tallest girl in her class.She can play the violin.（合成一句）可以说 She is the tallest girl that who can play the violin in her class.
问题描述：
.She is the tallest girl in her class.She can play the violin.（合成一句）
可以说 She is the tallest girl that who can play the violin in her class.
答
She is the tallest girl who can play the violin in her class.
答
She is the tallest girl （that） can play the violin in her class，是定语从句，*先行词只能用that，that引导并与从句，可省略
答
The girl (who can play the violin) is the tallest in her class.
会拉小提琴的那个女孩是她班上最高的.
把后一句变为前句的定语从句.
或者 The girl (who is the tallest in her class) can play the violin.
在班上是最高的那个女孩会拉小提琴.
这是把前句变为定语从句.