With apologies to Rover_KE, I am making another post here rather than editing my above post. The reason is I am unable to do so perhaps because I am using usingenglish.com through my mobile. There is no such option as 'edit post' with above post.
I wanted to say this. It appears that I haven't been able to get my message across to the teachers. Dear teachers, I just wanted know if the following interrogative sentences are natural.
(1) When do we use an infinitive
and when a gerund?
(2) Under what conditions do we use an infinitive and under what conditions a gerund?
(3) In what situations do we use and infinitive and in what situations a gerund?
(4) Under what circumstances do we use...
I am not asking to answer these questions. Rather, I want to know if these interrogative sentences are correct or not.