What is the main idea of the paragraph?
(30 points and brainliest for best answer)

another interesting advancement in green technology is the idea of green walls and green roofs, which are green because they are made from plants. using plants as part of the building is a great way to make a building green. green walls and roofs reduce the amount of cooling needed in the summer and heating needed in winter.

a) using low-flow toilets, sinks, and shower heads saves water.
b) gray water is any type of waste water other than toilet water.
c) xeriscaping is landscaping with plants that do not need much water.
d) using walls and roofs made of green plants reduce the amount of cooling needed in the summer.