How to introduce a secondary clause after a preposition?

When introducing a secondary clause, after a preposition use whether (not if).

For example, a phrase like this: There are doubts about whether climate change is real.
Solidify this grammar point right now
(you will be asked to create an account if you do not have one)

Learn more simple rules

Phrase the Cat inviting to practise English Phrase the Cat waving

At you can study grammar points and practise their application right away.