Despite their many similarities, Mars is different from Earth in several key ways. Mars is smaller than Earth and has a slower, more elliptical orbital path around the sun. That means a year on Mars is almost twice as long as a year on Earth. Mars has a weaker gravitational pull than Earth, and it has two moons called Phobos and Deimos. Perhaps the most crucial difference between the two planets is that Mars cannot support human life. The planet’s atmosphere is 95% carbon dioxide, which humans and other animals cannot breathe. Its landscape is barren, dry and susceptible to strong dust storms. It is extremely cold, with temperatures ranging from 0 to -100 degrees Celsius. The cold is a result of Mars’s additional distance from the sun and an atmosphere 100 times thinner than that of Earth, which allows heat to escape more easily.

Question

According to the passage, which of these is an important reason why humans cannot survive on Mars?

A
One Mars year is significantly longer than one Earth year.

B
Mars has two moons, and humans can only live with one moon.

C
Mars’s atmosphere is mainly carbon dioxide, which humans cannot breathe.

D
Mars has a weaker gravitational pull, which cannot support human life.

Answer 1

C Mars’s atmosphere is mainly carbon dioxide, which humans cannot breathe.