Which of the following propositions are so related that they cannot both be false though they can both be true ? Choose the correct answer from the options given below :

Statements 3 (Some pitcher-plants are carnivores) and 4 (Some pitcher-plants are not carnivores) cannot both be false though they can both be true.

Statement 3 is the particular affirmative (I) and Statement 4 the particular negative (O).

I and O are sub-contraries on the square of opposition.

Sub-contraries forbid joint falsity, since some are and some are not cannot both fail, yet they permit joint truth.

This not both false yet possibly both true pattern is the sub-contrary relation.