What impressed him most was their speed.

最令他钦佩的是他们的速度。

《柯林斯英汉双解大词典》

What impressed me most was something that happened during our military training.

让我印象最深的是军训期间发生的一件事。

youdao

I had to see her a few times, but what impressed me most were the magazines in her waiting room.

我不得不去看她几次，但最令我印象深刻的是她等候室里的杂志。

youdao

"What impressed me was his high level of energy.

VOA: standard.2009.09.16

I'm generally pretty impressed by what the, what my classmates have gotten up to before they came to school here.

我的同学在入学之前已经完成的事情让我印象深刻。

优秀的MBA人们 - SpeakingMax英语口语达人

"I was at the USA House the other day talking to somebody about our student group, and I went on after our discussion, and then he came back and he came over and shook my hand and said how impressed he was with what we were doing."

VOA: standard.2010.02.26

What impressed me most about the Big Data industry is something that I will shamelessly coin collab-petition.

FORBES: A Mind Blowing Big Data Experience: Notes From Strata 2013

What impressed me most about him was that he always wanted to improve.

BBC: World Cup scouting: attacking midfield

What impressed me most was how quickly the car accelerated.

FORBES: Fueling Hope