this is my first time using this website to ask a question. I hope you can help me!
I work as an English assistant teacher, and during a lesson, I pinged this sentence
“What we must do is helping him”
As incorrect. One of my co-teachers got it from a workbook. However, I couldn’t explain why this was incorrect, and I don’t have a lot of grammar experience. All I had was a ping that it sounded a bit incorrect to my ear. I offered either “What we must do is help him”, or “Helping him is what we must do” as alternatives. Due to the way the students are learning this grammar point, it is important that the “What” is at the start of the sentence.
Can anyone help with explaining how to fix “What we must do is helping him”? Or confirm if it’s correct or not? Thank you!