(1) The climate becomes colder when the amount of dust at high altitudes in the atmosphere Increases. (2) There are several
ways that dust may get into the atmosphere. (3) Volcanic eruptions can add so much dust that sunlight is scattered back to
outer space. (4) Chimneys, especially industrial smokestacks, also throw large amounts of dust Into the atmosphere. (5) The
burning of tropical forests to clear land for farming is another way the amount of airborne dust is increased. (6) Finally,
should a nuclear war ever occur, it might add so much dust to the atmosphere that it could cause a new Ice age-a nuclear
winter in which the climate becomes so cold that no new crops can be grown.
One source of dust in the atmosphere is
(A) a. sunlight.
(B) b. farming.
c. chimneys.
D) d. cold weather.