Three Statements are given followed by Three conclusions numbered I, II and III.
Assuming the statements to be true, even if they seem to be at variance with commonly known facts, decide which of the conclusions logically follow(s) from the statements.

Statements:
All plains are mountains.
No sea is a mountain.
Some valleys are seas.

Conclusions:
I. Some valleys are plains.
II. No valley is a mountain.
III. No sea is a plain.