In the late 1970's,many people in North America turned their attention to environmental problems ,and new steel -- and -- glass skyscrapers were widely criticized. Some ecologists  pointed out that a number of tall buildings in a city often overburden public transportation. Skyscrapers are also _ of electric power and water. In just one recent year, the addition of 17 million square feet of skyscraper office space in New York City itself has already raised the top daily demand for electricity by 120, 000 kw -- enough to supply the entire city of Albany in New York area for a single day. Glass--walled skyscrapers can also be especially wasteful. The heat loss ,or gain, through a wall of half  inch plate glass is more than ten times that through a typical ordinary wall filled with bricks or board. In order to decrease the pressure on heating and air -- conditioning equipment, builders of skyscrapers have begun to use double--layered glass ,and reflective glasses coated with silver or gold mirror films that could reduce glare  as well as heat gain. However, mirror -- walled skyscrapers may raise the temperature of the surrounding air and affect neighboring buildings as well. Skyscrapers put a severe pressure on a city's sanitation  facilities, too. If fully occupied, the towers just within the central area of New York would alone produce 2. 25 million gallons of waste water each year^--as much as the city size of Stanford, Connecticut, which has a population of more than 109,000. Glass walls of skyscrapers are specially mentioned in order to   _  .
show how skyscrapers manage to lessen their pressure explain why skyscrapers can control its air conditions describe further how wasteful skyscrapers could be present the stability of skyscrapers in modern buildings
Question: In the late 1970's,many people in North America turned their attention to environmental problems ,and new steel -- and -- glass skyscrapers were widely criticized. Some ecologists  pointed out that a number of tall buildings in a city often overburden public transportation. Skyscrapers are also _ of electric power and water. In just one recent year, the addition of 17 million square feet of skyscraper office space in New York City itself has already raised the top daily demand for electricity by 120, 000 kw -- enough to supply the entire city of Albany in New York area for a single day. Glass--walled skyscrapers can also be especially wasteful. The heat loss ,or gain, through a wall of half  inch plate glass is more than ten times that through a typical ordinary wall filled with bricks or board. In order to decrease the pressure on heating and air -- conditioning equipment, builders of skyscrapers have begun to use double--layered glass ,and reflective glasses coated with silver or gold mirror films that could reduce glare  as well as heat gain. However, mirror -- walled skyscrapers may raise the temperature of the surrounding air and affect neighboring buildings as well. Skyscrapers put a severe pressure on a city's sanitation  facilities, too. If fully occupied, the towers just within the central area of New York would alone produce 2. 25 million gallons of waste water each year^--as much as the city size of Stanford, Connecticut, which has a population of more than 109,000. Glass walls of skyscrapers are specially mentioned in order to   _  .
A. show how skyscrapers manage to lessen their pressure
B. explain why skyscrapers can control its air conditions
C. describe further how wasteful skyscrapers could be
D. present the stability of skyscrapers in modern buildings
Answer: