Why Are Search Strategies for Extraterrestrial Life Usually Based on a Carbon

Multiple Choice

Why are search strategies for extraterrestrial life usually based on a carbon chemistry?

A) Carbon dioxide is the main ingredient of planetary atmospheres,both terrestrial and Jovian.
B) Carbon is abundant and is versatile in forming complex,long-chain molecules.
C) Most meteorites that reach Earth are composed of carbon.
D) No other atom can combine easily with the abundant hydrogen and helium to form long molecules in interstellar gas.