Shorten the second part of the sentence by omitting unnecessary words.
Ellipsis is the omission of words that are understood from the context. It avoids redundancy by "leaving out" non-essential information. ellipsis and substitution grammar exercises pdf
Gapping
"Do you think the team will win?" "Yes, I think ." Answer: "Do you think the team will win?" "Yes, I think so." (Substitution) Shorten the second part of the sentence by
I wanted to help him, but I didn't know how . Answer: I wanted to help him, but I didn't know how. (Ellipsis) but I didn't know how. (Ellipsis)