单项选择题

Directions: There are five reading passages in this part. Each passage is followed by five questions. For each question there are four suggested answers marked A, B, C and D. Choose one best answer and blacken the corresponding letter on the Answer Sheet.
Passage One

Every summer in Australia there is the danger of bush fires. Long periods of hot dry weather cause the grass and trees to become highly inflammable. In addition to the dryness and high temperature, another important factor is the great amount of oil in the leaves of such trees as eucalyptus, gum and ti trees. Fires start very easily, often spontaneously(自动地，自发地), but usually because of a carelessly thrown cigarette or match. If there is a high wind, the ample supply of air fans the flames into an inferno. The radiant heat vaporizes the oil in the leaves; and the fire travels very quickly, sometimes overtakes fleeing cars and burns passengers to death. Great fires often occur around Christmas, in areas near big cities, causing great loss of life and property.

Bush fires travel （）