Question

. We had to turn _______ their invitation to lunch as we had a previous engagement.

A. over B. out C. up D. down

Answer 1

D. down

“Turn down” is the term for declining an offer/invitation.

Let’s see the sentence with the word included:
We had to turn down their invitation to lunch as we had a previous engagement.
It is basically saying that they declined an invitation to lunch as they had their previous engagement.

I hope I helped!

Answer 2

We had to turn b.out their invitation to lunch as we had a previous engagement.

their invitation to lunch as we had a previous engagement.

A. over B. out C. up D. down