我不得不谢绝他的邀请，因为我另有约会。

I had to decline his invitation because I had another appointment.

youdao

然而我有些应接不暇，因为我在几小时之内就得到了回复，于是不得不谢绝了一些志愿者工作机会，因此记住这个。

I was actually inundated with replies within hours and had to turn down a number of volunteering opportunities, so bear this in mind.

youdao

我恐怕不得不谢绝你的邀请。

I am afraid I have to decline your invitation.

youdao