Please choose the correct answer to the question: The atmosphere of Mars is almost entirely composed of a greenhouse gas. Compared with Earth, which factor accounts for the low, nighttime surface temperatures on Mars?

Answer1: Mars is much farther from the Sun than Earth. Answer2: The atmosphere on Mars has an extremely low density. Answer3: The atmosphere on Mars lacks global circulation. Answer4: Mars has more glacial activity than Earth.

Answer format: answer1/answer2/answer3/answer4
Answer: answer2