Hi, I'm a new member.
My apology if the question has been discussed in the past.
(1)(2)(3)sound natural, but some native speaker friends say (5)(6)don't. How so?
(5)(6)look like the same sentence structures as
(1)What you heard from Dan is not quite true.
(2)What is written here is full of mistakes.
(3)Pay attention to what he says.
*(5)What you can do is to help her.
*(6)What you can do is helping her.