第8题: [单项选择]A tide is called diurnal when（）. A. only one high and one low water occur during a lunar day B. the high tide is higher and the low tide is lower than usual C. the high tide and low tide are exactly six hours apart D. two high tides occur during a lunar day 参考答案:A
A. explain different types of weather B. show that tornadoes occur frequently in Canada C. indicate the tornado are common in summer D. give an example of a damaging storm 参考答案:D 答案解析:细节理解题。本文第一段的前半部分提到加拿大Edmonton龙卷风，是为了更具体地说明破坏性的风暴。故选D项。
第29题: [单项选择]Ⅲ型限制性内切核酸酶( )。 A. 由两个亚基组成，仅识别半甲基化位点 B. 甲基化和限制活性相互排斥：MS亚基促使甲基化，R亚基促使限制 C. 由两个亚基组成，在识别位点附近识别并进行甲基化或限制 D. 在错配修复中起关键作用，因为酶结合到DNA上是以结构扭曲为基础，而不是序列错误识别 参考答案:C
