Water is a major contribution to weathering. In a dry place, there will be not as much water to erode away small pieces of rocks, rust certain objects, or seep into the cracks of rocks to freeze and expand. Also, molecules in the air move much slower when the temperature is cold compared to when it is warm
"Keep", "factor", and "calculate" are all verbs in the list of things the new system allows teachers to do. The other sentences are inconsistent with their list of verbs/adjectives/nouns. Thus, option A is the only one that is grammatically correct.
