Which of the following statements are so related that they cannot both be true but could both be false?

1.All biologists are outstanding teachers

2.Some biologists are outstanding teachers

3.No biologists are outstanding teachers

4.Some biologists are not outstanding teachers

A2 & 4 only

B1 & 4 only

C1 & 3 only ✓ Correct

D3 & 4 only

Correct answer: (C) 1 & 3 only

Explanation

Statements 1 and 3 are contrary to each other.

Statement 1 "All biologists are outstanding teachers" is an A proposition.

Statement 3 "No biologists are outstanding teachers" is an E proposition.

A and E are contraries on the square of opposition.

They cannot both be true, but both can be false together.

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