Why Is the Strategy of Searches for Extraterrestrial Life Usually

Why is the strategy of searches for extraterrestrial life usually based on carbon chemistry?

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