In paragraph 3, the author mention both demolition and...

Câu hỏi: Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the following questions.
The concept of being environmentally conscious, or "green", has become more prevalent in twenty first-century U.S culture. It has begun to affect the manufacturing of everything from non- toxic household cleaning products to motor vehicles powered by alternative sources of energy. However, one way of being "green" that is perhaps not as apparent to the viewer but of equal importance in being environmentally conscious, is the construction of buildings that are considered "sustainable". Sustainable buildings are those that do not impose on the environment or rely on the over-utilization of energy or natural resources. There are four main principles of sustainability, which includes consideration of the health and stability of all living things and their environmental diversity, as well as the economic opportunities of humanity.
Sustainable architecture consists of environmentally conscious design techniques. In the past, the demolition of an old building meant that all or most of the debris of the building would end up in a landfill or a waste disposal site. Today, architects can plan and design a building that uses recycled materials, such as wood, concrete, stone, or metal. These materials are salvaged from the demolition of an older building and can be appropriately incorporated into a new construction. Architects and construction supervisors may also choose to recycle more organic parts of demolished buildings, such as wooden doors, windows and other glass, ceramics, paper, and textiles.
A problem that has often arisen has been with how a site crew-whether it is demolition or
construction crew determines and sorts what is "waste" and what is recyclable. Architects and environmental scientists have to decide whether or not a material is appropriate for use in new construction and how it will impact the environment. They must evaluate the materials from the demolition and determine what those materials contain, and if they meet the standards set by the U.S, government's Environmental Protection Agency (the EPA). If the debris from the demolition contains hazardous materials that are harmful to the environment or to the consumer, such as asbestos, then the material is not salvageable. Use of the asbestos for insulation and as a form of fire retardation in buildings and fabrics was common in the nineteenth century. Asbestos was once used in shingles on the sides of buildings, as well as in the insulation in the interior walls of homes or other construction. In new "green" construction, insulation that once asbestos- based can be replaced with recycled denim or constructed with cellulose-a fibrous material found in paper products. The same-assessment applies to wood or wallboard painted with toxic lead-based paints. In addition, gas-flow regulators and meters on both water and gas heating systems constructed prior to 1961 must be carefully evaluated to determine that they do not contain dangerous substances such as mercury. Mercury can be harmful to humans and the environment if it is spilled during the removal of these devices.
In paragraph 3, the author mention both demolition and construction crews in order to___________
A. give an example of how choosing materials is not easily determined on a site
B. illustrate the types of crews that sort waste and recyclables
C. demonstrate that choosing recyclable materials is challenging for both crews
D. contrast the work of the two types of crews on a site