Question

_____, the game had to be called off due to the weather.

A. Regrets
B. Regretful
C. Regrettably
D. Regretting

Answer 1

I think. it. shall. be. Regretably

Answer 2

The answer of the above question will be - “Regrettably, the game had to be called off due to the weather”

The term regret is used for the disappointment or sadness of some sort.

Here people were sad that the match is cancelled because they were looking forward to it.

Since it is in the start of sentence hence the form will change.