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.Which of the following is an assumption on which the argument depends?
【选项】The alarms were installed at the time of year when harbor porpoises are most plentiful in the Massachusetts waters.