IMO the answer should be A.

Although those particles are a benefit "they benefit the earth", they are also a disadvantage "they also accelerate"

"acting as global thermostat..." is an explanation of what results from the reflection and absorption of solar radiation and this need not be parallel with the other attribute that is the acceleration of the destruction of ozone layer.

OA please...

IMO A

B is incorrect because...."...keeping Earth either from burning up or freezing over.....".

both element of EITHER should be parallel.

The correct form must be "FROM either burning up or freezing over...."

A uses correct form

IMO: E
paralell: they act.... they also accelerate.
either burning up or freezing over

it's A . Although is already showing contrast ,so you don't need while or any contradicting conjunction here and acting as global clearly show causal behavior ..
either X or Y is correct here .