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  3. Tides are created mainly by the pull of the moon on the earth. The moon’s pull causes water in the oceans to be a little deeper

Tides are created mainly by the pull of the moon on the earth. The moon’s pull causes water in the oceans to be a little deeper

admin2014-03-15  67
问题     Tides are created mainly by the pull of the moon on the earth. The moon’s pull causes water in the oceans to be a little deeper at a point closest to the moon and also at a point farthest from the moon, on the opposite side of the earth. These two tidal "waves" follow the apparent movement of the moon around the earth and strike nearly every coast line at intervals of about twelve hours and twenty-five minutes. After reaching a high point, the water level goes down gradually for a little more than six hours and then begins to rise towards a new high point. Hence, most coast lines have two tides a day, and the tides occur fifty minutes later each day. Differences in the coast line and in channels in the ocean bottom may change the time that the tidal wave reaches different points along the same coast line. The difference in water level between high and low tide varies from day to day according to the relative positions of the sun and the moon because the sun also exerts a pull on the earth, although it is only about half as strong as the pull of the moon. When the sun and the moon are pulling along the same line, the tides rise higher, and when they pull at right angles(直角)to one another, the tide is lower. The formation of the coast line and variations in the weather are additional factors which can affect the height of tides. Some sections of the coast are shaped in such a way as to cause much higher tides than in other areas. A strong wind blowing towards the shore may also cause tides to be higher.
Which of the following may be concluded from the information presented in the passage?
选项 A、Some coast lines do not have two tides each day.
B、Tides usually rise to the same level day after day.
C、Tides are not affected by the shape of coast line.
D、The sun has as much effect on tides as does the moon.
答案A
解析 根据文章中的第5句“因此，大部分海岸线每天有两次潮水，而且潮水涌来的时间每天落后50分钟”，因此，不难推断出有些海岸线不是每天有两次潮水。
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