Although ice particles in the upper atmosphere benefit Earth in that they reflect and absorb solar radiation, acting as a global thermostat and thus keeping Earth from either burning up or freezing over, they also accelerate the destruction of the ozone layer by reacting with chlorofluorocarbons (CFC's).A. acting as a global thermostat and thus keeping Earth from either burning up or freezing over, they also accelerateB. acting as a global thermostat and thus keeping Earth either from burning up or freezing over, while also acceleratingC. act as a global thermostat and thus keep Earth from either burning up or freezing over, while also acceleratingD. they act as a global thermostat that thus keeps Earth either from burning up or freezing over, even though it also acceleratesE. they act as a global thermostat to thus keep Earth from either burning up or freezing over, but they also accelerate

The second part of the sentence provides an added role of the ice particles while the last part of the sentence gives the demerit of these ice particles. The whole sentence depends on the independent clause which is the last part of the sentence.

So, the form of the sentence is correct with the middle part adding an extra detail of the subject, while also completing the meaning of the whole sentence. The sentence needs no change.

Thus, the correct answer is option (A).