at a time

　each time 每次

　break down

　lose effectiveness 失效

　in fine / bad shape

　be in good / bad condition 状况良好／不佳

　scuba diving

　the sport of swimming under water while breathing through a tube that is connected to a container of air on your back 戴自携式潜水呼吸器潜水

　set out (to do something)

　begin a job, task, etc. with a particular aim or goal 着手 (做)

　stop short

　stop suddenly 突然停下

　turn to

　shift to 转向，转为

　Boston University

　波士顿大学

　Christopher Reeve

　克里斯托弗·里夫 (美国演员，因扮演“超人”而闻名)

　Toronto

　多伦多 (加拿大城市)

　Virginia

　弗吉尼亚 (美国州名)