Correct option is A
Statement Analysis:
Some stars are planets: Intersection exists between Star and Planet.
No planet is a comet: Complete separation between Planet and Comet.

Conclusion Analysis:
Conclusion I (Some stars are not comets): True. The specific part of 'Stars' that is inside 'Planets' can never be 'Comets' because No Planet is a Comet.
Conclusion II (All comets are planets): False. This contradicts the statement "No planet is a comet."
Final Answer: Only Conclusion I follows.