What Is the Status of the Greenhouse Effect on Mars

Multiple Choice

What is the status of the greenhouse effect on Mars at the present time?

A) It no longer exists at all.
B) It is very weak and raises the planet's temperature only a few degrees above the temperature it would have with no atmosphere at all.
C) It is weak but becoming stronger as Martian volcanoes continue to dump large amounts of CO₂ into the atmosphere.
D) It is very strong and has caused the temperature to be at least 100 degrees above the temperature it would have been with no atmosphere at all.