What is the main idea of this passage? a) in order to preserve and protect our environment, builders should construct more "green" buildings. b) one way a building can be more green is by the use of passive solar heating to decrese the use of electricity. c) reducing the amount of fresh water used in building is another way that builders can protect the environment. d) one way a building could be more green is through the use of green roofs and walls to reduce heating and cooling costs.