To prevent harbor porpoises from getting tangled in its nets and suffocating, a fishing company installed acoustic alarms on all its boats that fish in waters off Massachusetts. The sound emitted temporarily disorients the porpoises and frightens them away. Since the installation of the alarms, the average number of porpoises caught in the company's nets has dropped from eight to one per month. The alarms, therefore, are saving the lives of harbor porpoises in those waters.
BD的选项恰恰就是assumption和support的区别。Assumption是要回答why，为什么能达到这个目的，是因为alarm可以让鱼避免被撞上，D其实应该是support结论，也就是说从eliminate他因加强结论，alarm的确有用，旁支支持
Which of the following is an assumption on which the argument depends?
(A) The use of acoustic alarms increases the number of commercial fish caught by the fishing company's boats.
(B) When disoriented, harbor porpoises are not significantly more likely to be killed by other boats.
(C) Environmentalists advocate the use of acoustic alarms as a means of protecting the harbor porpoise population.
(D) The alarms were installed at the time of year when harbor porpoises are most plentiful in the Massachusetts waters.
(E) The cost of installing acoustic alarms on fishing boats is less than the cost of repairing nets damaged by harbor porpoises.