In 1971, hot on the heels of plate-tectonic theory's acceptance, J. W. Morgan suggested that hotspots—areas of intense volcanism such as Hawaii, Yellowstone, and Iceland—are fueled by plumes of hot material arising in the deep mantle and punching through the mobile shallow mantle and crust to the surface. Morgan's theory was developed to explain the time-progressive trails of volcanoes associated with some hotspots and the hotspots' apparent fixity relative to one another. If the sources of the volcanism were rooted in the immobile deep mantle, they would not move relative to one another and the plates at the surface would drift above, bearing away trails of volcanism. According to a recent article by geologist G. R. Foulger, however, although hotspots do exist, they do not have time-progressive volcanic trails and are not fixed relative to one another.
本文開篇給出JW觀點認為hotspot是由plumes of hot material加熱的。第二句說這個理論解釋了火山的時間序列。第三句是論證的假設，即如果火山的扎根在不動的地幔中，那么他們將不會彼此關聯并且板塊也會漂移，使得火山飄走。第四句給出結論說盡管hotspot存在，但是不能解釋火山的時間序列。
Which of the following best describes the function of the highlighted sentence?
A. It points out some unintended consequences of a theory.
B. It elucidates the thinking behind Morgan's suggestion.
C. It explains why the theory of plate tectonics had been accepted.
D. It expresses the author 's attitude toward Morgan's suggestion.
E. It introduces an alternative to Morgan's suggested explanation.
Springtown’s fire department wants the town council to buy it another ladder truck. These trucks are useful in fighting fires in high-rise buildings. The town council argues, however, that Springtown has only two high-rise buildings, and it already owns enough ladder trucks to fight any fires there. So, they say, Springtown does not need another ladder truck.
The town council's argument assumes that？
A. Springtown cannot afford to buy another ladder truck.
B. Springtown's high-rise buildings all meet or exceed current fire safety standards.
C. the number of high-rise buildings in Springtown is likely to grow.
D. at least one of Springtown's ladder trucks is not due to be permanently removed from service in the immediate future.
E. it is possible to fight fires successfully in high-rise buildings without using ladder trucks.