Help Marco finish his panicked text to his project partner!

"Oh no! I completely forgot ___ the presentation slides to the group chat!"

The correct answer is to attach.

When we use "forget" + "to" + infinitive (to attach), it means you didn't do something you were supposed to do. If you use "forget" + gerund (attaching), it means you did it, but you lost the memory of doing it! Marco didn't do the action, so he needs the infinitive.