I am sorry, I cannot guarantee, but I will do my best.

对不起，我不能保证，但是我会尽最大努力。

youdao

I'm sorry I cannot guarantee, but I'll do my best.

对不起，我不能保障，但我一定会尽我全力去做。

youdao

I cannot guarantee anything, but please be assured that we'll try our best.

我不能保证，但请放心我们一定尽力。

youdao

I am regret we cannot guarantee, but we will try our best.

很遗憾我不能保证，但我们一定尽力而为。

youdao

I am regret we cannot guarantee, but we will try our best.

很遗憾我不能保证，但我们一定尽力而为。

youdao