An Important Advance in the Search for Life Elsewhere in the Solar

An important advance in the search for life elsewhere in the solar system was the:

A) discovery of primitive life-forms on Mars.
B) replication in laboratories of silicon-based substitutes for the most important carbon-based life molecules.
C) discovery of liquid water on Europa, Ganymede, and various other places in the solar system.
D) discovery in meteorites of the remains of microbes.