Which of the following best explains why Mars' and Venus' surface temperatures vary, despite both planets having atmospheres that contain mostly carbon dioxide?

Question

Mars has a thin atmosphere that cannot hold much heat.
Mars has a thin atmosphere that cannot hold much heat.

Venus has a thick atmosphere which blocks heat from the surface.
Venus has a thick atmosphere which blocks heat from the surface.

Venus has a surface of high mountains which absorb heat.
Venus has a surface of high mountains which absorb heat.

Mars has a surface of red rocks and sand which reflect heat.

Answer 1

The best explanation for why Mars' and Venus' surface temperatures vary, despite both having atmospheres that are mostly composed of carbon dioxide, is:

Mars has a thin atmosphere that cannot hold much heat.

Venus has a very thick atmosphere, which creates a strong greenhouse effect that traps heat and results in extremely high surface temperatures. In contrast, Mars has a much thinner atmosphere, which is less effective at retaining heat, leading to cooler surface temperatures.