Infinitive vs Gerund

[Lone]

Dear Alan,

Merry Christmas!

1. Don't forget (a. inviting, b. to invite, c. invite) your husband to the office party.
The answer is b. to invite, am I right?

2. Don't forget (a. setting, b. to set, c. set) your alarm clock. We've got to get up early tomorrow.
The answer is a. setting. Is it correct?

If I am right in both questions, could you please tell me what factor(s) determine the choice of infinitive/gerund in the 2 seemingly similar sentences?

Thanks!

Lone

[Alan]

And a merry Christmas to you, too!

Regarding your question, the infinitive is correct in both cases (so 'to set' in #2).