The information used by the computer to make its detailed maps ______. Ⅰ. was gathered by the Defense Department and the U. S. Geological Survey Ⅱ. shows points roughly 200 feet apart Ⅲ. involves altitude measurements

A．The computer simulates rays of the sun, filling in areas of light and shadow.
B．Lines radiate outward from the imagined observer and a dot of color is placed where the line intersects with one of the points of altitude in the machine's memory.
C．X-rays are used to trace the outline of the terrain through buildings and trees.
D．The exact movement of rays is used by private detectives to solve mysteries and locate missing persons.

A．available information about the weather
B．surrounding land area
C．blank spaces between the mountain ranges
D．amount of forest per square mile