Which sentence could be added to the passage to support the main idea? a. other planets, seen through telescopes, show signs of volcanic activity, much like our Earth.
b. recently, water has been discovered on Mars, making it seem more possible that life could exist there.
c. also, the Earth's tilt and its distance from the sun means we have mild seasons that humans can withstand.
d. probes we have sent into space have brought back data on other planets that are too far to ever visit.