Unit 2 The United Kingdom课时作业

Learning about language

Ⅰ. 阅读理解

A

(2019·邯郸模拟C)Have you ever noticed tiny raised areas on the branches of a tree？These may have been insects. These small insects feed on tree sap(汁液)．Insects on urban trees are notably more abundant than those on rural trees. As a result，urban trees suffer from heavy infestations(害虫横行)，and are often unhealthy or die. To protect and restore urban trees' health，we need to determine the factors that make these tree pests more successful in urban habitats.

Living organisms interact closely with their environment. The warmer，more drought－stressed trees harbor more successful pests than cooler，less drought－stressed trees. As cities and natural habitats become hotter and drier，damaging insects will become more abundant on urban trees.

Trees within urban forests are valuable economically and for the environmental sustainability(可持续性)of the region. More than half of the world's population lives in cities. Across the globe，people are moving into cities at a faster rate than ever. Rapid growth may turn cities into places with harder conditions. Although cities are primarily made of buildings，roads，parking lots，and vehicles，there are still plants in them. The trees within a city are referred to as the urban forest. Urban forests offer very big benefits to human and environmental health. They improve air and water quality，provide habitat for wildlife，cool down temperatures and beautify our environment. They make cities livable.

However，being a city tree is not easy. Heat released by human activities is trapped in cities. As a result，temperatures in urban areas are often warmer than their surrounding rural areas. We call this urban warming or the urban heat island effect. Urban habitats are mostly made of surfaces of asphalt(沥青)and concrete. These surfaces reduce the amount of rainwater that reaches tree roots. As a result，urban forests may suffer，which can negatively affect people and the environment.