What Role Has Methane Played in the Search for Life

What role has methane played in the search for life on Mars?

A) Methane destroys simple life-forms, so the existence of methane precludes the existence of simple life-forms on Mars.
B) Methane is produced by life-forms, so the search for methane being released from under the Martian surface-so far unsuccessful-continues.
C) Sunlight breaks down methane within a few centuries. The presence of methane on Mars suggests that it is being renewed continually, perhaps by living organisms.
D) So far methane has played no role in the search for life on Mars.