Many teachers believe that hands－on experience is the ____(good) way to learn. A group of students in the United States are putting that belief to the test. They ____ (success) designed and built a robot for discovering unexplored mines ____ the bottom of the sea. Students made the robot ____(answer) a challenge from the U．S. Department of Defense.

    The students recently tested the underwater vehicle ____(call) PerseusⅡin a 95－meter－long tank of water at the Stevens Institute of Technology.

    The robot costs about $15,000 to build. The students use a video game control to direct ____(it) movements in the tank. What's more, devices known as Japters ____ (able) the robot to go up, down and toward its target in the water. Video cameras on the robot send images back to a computer through a 13－meter－long cable. Perseus Ⅱ,____the students worked up to 20 hours a week to design and build, also has ____ set of lasers (激光), which are used to measure the size of an object.

    DeLorme supervised the project from ____(begin) to end. He says the specialized requirements of robots were demanding.

阅读下列材料

材料一  我们现在应当非常谨慎，应当不采取对卷入冲突中的国家的防务不会有益而不只会使人激怒，甚至会挑起致命步骤的措施。

——摘自1962年赫鲁晓夫至肯尼迪的信

材料二  美国将参加各盟国和朋友的防务和发展活动，但是美国不能而且也不会制定全部方案，拟定全部计划，执行全部决定，负起保卫世界自由国家的全部责任。只有在我们的帮助真正起作用，并且被认为是符合我们的利益的时候，我们才会给予帮助。

——摘自1970年尼克松的对外政策报告

材料三  美国在欧洲、太平洋、中东以及其他美国疆界之外的地区，有着广泛的义务和安全利益。这就需要美国担当起“强有力的”、“令人信服”的“领导责任”。、

——摘自里根的讲话

请回答：

根据短文理解，选择正确答案。

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The light went off suddenly. Everything__________ very dark.