The moon does not have atmosphere. why?

One characteristic of the moon of Earth is that it basically has no atmosphere. The Earth has an atmosphere rich in Nitrogen and Oxygen but on the moon the surface is directly exposed to outer space. There are three reasons why the moon has no atmosphere. The primary reason is because the moon is too small. Compared to the Earth, the moon is about 1/4th the size. This reduces the amount of gravity on the moon. Strong gravity is needed to hold an atmosphere into place. With weak gravity, gases that are emitted from the surface quickly are lost to outer space. Another reason is because the moon does not currently experience plate tectonics and geologic upwelling. Plate tectonics allows for a recycling of crust and convergence and divergence of plates occurs and this leads to volcanoes and gases escaping at the boundaries. The moon is said to be geologically dead. There are currently no significant processes that allow for abundant gases to supply an atmosphere. The early moon may have had an atmosphere when it was geologically active but the crust of the moon is currently “frozen” into place and thus there are very little gases being emitted as compared to Earth. Another reason is because the moon is relatively close to the sun. This reason is tied closely to the moon having weak gravity. The solar wind from the sun helps strip away a weak atmosphere. Earth and Venus do not suffer the same fate since the gravity is high enough to hold the atmosphere in place. There are other moons in the outer solar system that are better able to hold an atmosphere due to being further away from the sun among other reasons.  

Explanation:

i wanna say it’s between b and d, leaning more towards b.