Mirror: something is the reason for something else

Something is the reason for something else.
Something is the main reason for something else.
Something is one of the main reasons for something else.
Something is one of the main reasons why something else still happens.

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President's change of heart over the social issues was the main reason for his profound disagreement with his own party's lawmakers

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Mirror: A Noun is a noun predicate(reason for, etc.) + another Noun.