Urban development is having a direct impact on the weather in many cities worldwide. It has been noticed that the difference in temperature is usually greater at night and the phenomenon occurs in both winter and summer. Experts agree that (631) _____________ when open green spaces are replaced with asphalt roads and tall brick or concrete buildings. These materials retain heat (632) __________ by the Sun and release it through the night. In Atlanta, in the US, this has even led to thunderstorms which occur in the morning rather than, as is more common, in the afternoon.

           Large cities around the world are adopting strategies to combat this issue and it is not uncommon to find plants growing on top of roofs or down the walls of large buildings. In Singapore, the government has (633)______ to transform it into a "city within a garden" and, in 2006, they held an international competition calling for (634) ____________ to develop a master plan to help bring this about. One outcome was the creation of 18 "Supertrees" – metal constructions resembling very tall trees. Each one is a vertical freestanding garden and is home to exotic plants and ferns. They also carry solar panels used to light the trees at night and (635) ___________, making them truly self-sufficient.

(Adapted from "The Official Cambridge Guide to IELTS")

Experts agree that (631) _____________ when open green spaces are replaced with asphalt roads and tall brick or concrete buildings.