The greenhouse effect: select one:
a. occurs when gases in the atmosphere direct the sunâs heat into the atmosphere.
b. occurs when gases in the atmosphere reflect the sunâs heat back down to earthâs surface.
c. occurs when gases in the atmosphere direct extra heat out into the atmosphere.
d. none of the above

The greenhouse effect is a natural phenomenon that enables life to propagate in Earth. During the day, the Sun provides energy through sunlight. Note that the Sun's energy is obtained from the nuclear fusion of hydrogen to helium. So, sunlight contains radiation at very high temperatures. In order to regulate heat, the atmosphere allows only some of the heat to be absorbed into the surroundings, but blocking the rest and reflecting it back to space. During night time, without the Sun giving energy, greenhouse gases in the atmosphere has 'reserved' heat that is trapped in the atmosphere. So, the greenhouse gases (like water vapor and carbon dioxide) maintains the average temperature of the Earth's atmosphere at around 33°C.

Therefore, the answer is letter B.

A. to determine if humans can explore mars safely

Decrease the surface area of the object and also decrease the concentration which will allow the particles to collide faster