Greetings, Depriya De, It's never a good sign when your parents stop trusting you is an example of an extraposition . A simple rule for deriving a sentence with subject extraposition from one of more orthodox ordering is: subject + predicate ~ it + predicate + subject Eg: Some grammarians apply the rule above to a type of sentence you mention. What they get is: When your parents stop trusting you + is never a good sign ~ It + is never a good sign + when your parents stop trusting you Now, you ask whether it is a nominal clause or an adverbial clause.
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