Agnes suggested sending off a balloon with a message to Jenny.
The phrase sending off puzzles me. I know it’s a verb phrase, but I don’t understand why it ends on -ing. Is it a noun or a verb?
I've looked at -ing words and spent some time thinking about how they are used. Normally, we use them as verbs with a form of to be, but there is no am or is here. When you Google "sending off", you get something about rugby, or it shows you send-off. But those are probably not the same thing. It's hard to find the right words to search for. I don't know how to proceed.