Which of the following explain why mars does not have a balanced greenhouse effect?
a. mars has an iron-rich core.
b. most of the water is locked in a permafrost layer underground.
c. plate tectonics prevents the release of carbon back into the atmosphere.
d. there are no active volcanoes sending carbon dioxide back into the atmosphere

d. There are no active volcanoes sending carbon dioxide back into the atmosphere

Explanation:

The mars today does not have any active zones of volcanoes as the heat gets trapped inside the planet when its forms have been lost as the outer crust of mars. Thus leading to this the impact of greenhouse gas that balances the system does not prevail. As the outer crust of mars is very thick to allow any kind of molten rock from deep below to reach the surface. But long ago, it used to have some kind of volcanic activity.

Ithink it's a, but i might be wrong