If one of two contraries is false, then the truth value of the other is

ATrue

BFalse

CNeither true nor false

DDoubtful ✓ Correct

Correct answer: (D) Doubtful

Explanation

If one of two contraries is false, the other is doubtful.

Contraries can both be false at the same time.

So falsity of one does not settle the other's truth value.

If "All S are P" is false, "No S is P" may be either true or false.

The undetermined value of the second is what "doubtful" names.

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