Two statements are given, followed by four conclusions numbered I, II, III and IV. 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:
No fish is a pen.
All keys are pens.

Conclusions:
I. No key is a pen.
II. No pen is a key.
III. Some pens are keys.
IV. Some keys are fishes.