A green roof is a roof of a building that is covered with vegetation over a waterproof membrane  . It is a proper method of growing plants on the roof and does not refer to the mere green color of the roof. People benefit a lot from these green roofing systems, and they are gaining popularity day by day. Human beings have occupied major areas of land and transformed them into huge buildings, which has severely affected the environment and the natural habitat of bird and insects. Green roofing compensates for that. It creates a natural habitat for creatures like bees, grasshoppers and other insects. Modern roofs need a lot of energy to control the temperatures in winter and summer. However, green roofs reduce the amount of energy required for controlling temperatures, thus making them energy-efficient. As green roofing is highly energy-efficient, it can act as a encouragement for people who are interested in green roofing systems and their benefits. It will increase the market value of the building and fetch the owner a great share of profit. As the vegetation requires a water supply, there is a inbuilt water preservation layer in the green roof system. This layer helps to keep the rainwater. It makes full use of the rainwater and prevents wastage. During heavy rains, the water runs off the flat roof. The green roof prevents this overflow by slowing down the volume of running water. Green roofs can compensate for the lost greenery in urban areas and increase the artistic value of an area. Your building will look beautiful, coated with green vegetation. Green roofs can serve as local community garden and create a natural atmosphere, giving physical and psychological benefits like reducing stress levels in people and keeping them physically fit. Besides, people can start their own small-scale cultivation  and experience the pleasure of gardening. Mr. Black who owns two buildings is interested in the green roofing system probably because  _  .
it can solve the problem of air pollution it produces more energy to power the buildings it creates natural habitats for birds and insects it can save him spending a lot of money on energy