单选题 .  Computers may one day turn night into day—with good old, natural sunlight.
    Colossal computer-controlled mirrors, thousands of feet across, may one day orbit the earth, reflecting sunlight onto a darkened United States.
    Some scientists say that 16 of these mirrors, each about a half mile across could aim their reflected light at one area on the earth that was about 200 miles by 300 miles. That much light would equal about 56 moons.
    The mirrors would be so high that they could catch the sun's light as it was shining on the other side of the earth. The mirrors could orbit—thousands of miles high—at the same speed as the earth turns on its axis (轴). That way, the mirrors would always be over the same spot.
    The aluminum-coated (涂铝的), plastic mirrors could be folded up and packed into a space-ship, according to the scientists. Once released a few hundred miles in space, the mirrors, powered by a solar-powered engine, could make the rest of the trip into space on their own.
    The scientists say that the computer-controlled mirrors could also be made to tilt (倾斜) slowly, so the reflected sunlight would sweep slowly along the surface of the earth. For example, as night fell, the mirrors could be tilted to light up Boston. Later on, as darkness spread slowly west-ward, Chicago, for example, then San Francisco could be lit up. The reflected sunlight would allow these cities to save up electricity. And in emergencies, such as power-failures, the mirrors could light up the affected area.
    What no one knows yet is what effect this artificial daytime would have on plants, animals, and humans. Would it confuse some animals and harm plants that are used to regular day-night cycles? The scientists recommend that studies be done to find out what bad effects there might be.1.  The word "colossal" in Para. 2 most likely means ______.