I saw someone post on Facebook and one of the commenter suggested the correction. I.e the original sentence is:
This question often comes to my mind whenever I study any subjects.
The person, suggested that the poster should have used singular like this
This question often comes to my mind whenever I study any subject.
Could you tell me the reason behind this? Beforehand, I've read this discussion and one of the answerer said that using singular is appropriate when the singular is followed by (how, what, which, etc). In this case, after the singular, it's ended by a period.