Which of the following statements are so related that they both cannot be false, although they may both be true?

1.All animals are birds

2.Some animals are birds

3.No animals are birds

4.Some animals are not birds

A1 & 3 only

B1 & 2 only

C3 & 4 only

D2 & 4 only ✓ Correct

Correct answer: (D) 2 & 4 only

Explanation

Statements 2 and 4 are subcontraries, which cannot both be false.

Statement 2 "Some animals are birds" is an I proposition.

Statement 4 "Some animals are not birds" is an O proposition.

On the square, I and O are subcontraries: at least one must be true.

They may still both be true, so both false is impossible while both true is allowed.

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