Use of comma before "Which" and "When"

When do I have to use a comma before “Which” and “When”? :roll:

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Use a comma before ‘which’ when it introduces a non-restrictive subordinate clause. Offhand, I don’t think I ever use a comma before ‘when’.
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Hi,

You might be interested to read some material I’ve written for the site on the use of the relative pronouns -

english-test.net/lessons/21/index.html
english-test.net/lessons/22/index.html
english-test.net/lessons/23/index.html

Alan

:lol: Thank you for your explanation