Is it who that impress you most ?
解释一下: is it who 是谁
后边that可以去掉 用来引导一个从句 impress you most (最使你印象深刻)
当然不只这一种翻译方法,好多。
who (had/have) impressed you most? 最简单。。。。
不懂问我 希望你我英语共同进步!
Who has made a deep impression on you?
Who has deeply impressed you?