If the statement 'Some birds are not mammals' is given as true, which of the following statements can be immediately inferred to be false?

ASome mammals are not birds

BSome birds are mammals

CNo birds are mammals

DAll birds are mammals ✓ Correct

Correct answer: (D) All birds are mammals

Explanation

The false one is 'All birds are mammals'.

The given true proposition is the particular negative O: Some birds are not mammals.

The contradictory of an O is the universal affirmative A.

Contradictories cannot both be true, so if O is true A is false.

Hence 'All birds are mammals' must be false.

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