Statements : Some mountains are hillocks. Some mountains are rivers. Some mountains are valleys. Conclusions : I. All mountains are either hillocks or rivers or valleys. II. No valley is river. III. Some river are valleys.

Answer: Option C

Since each combination of premises shall contain two particular premises, no definite conclusion can be drawn. However, II and III are statements involving the extreme terms of the last two premises and form a complementary pair. Thus, either II or III follows.