单选题 28. In the shallow end of Lake Tomwa, there are remains of numerous Jeffery pine trees that grew there during a lengthy drought. Researchers had believed that this drought lasted at least 150 years, but carbon dating reveals that pines were growing in the lake bed for only 120 years, from 1200 until 1320. Since the Jeffrey pines, which cannot survive in water, must have died at the end of the drought, the dating shows that the drought lasted less than 150 years.
The argument given relies on which of the following assumption? ______

A、 No other species of tree started growing in the bed of Lake Tomwa after 1200.
B、 No tree remains of any kind are present at the bottom of deeper parts of Lake Tomwa.
C、 There was at least one tree in the lake bed that was alive for the entire period from 1200 to 1320.
D、 There has not been a more recent drought that caused a drying up of the shallow end of the lake.
E、 The shallow end of the lake had been dry for less than 30 years by the time Jeffrey pines started growing in the lake bed.

【正确答案】 E

【答案解析】 E：选项取反。在杰弗瑞松树出现之前，湖水干旱的时间已经超过30年了→再加上之后松树的120年→湖水干旱时间超过150年，而原文的结论是不到150年，因此该选项取反之后推翻原文，正确。
A：文章只讨论杰弗瑞松树能否用来证明干旱时间，而且发现的残留物也只有杰弗瑞松树，和其他树木物种没关系。
B：讨论其他种类的树，无关。
C：这些杰弗瑞松树生长在1200年至1320年的120年间是文中已提及的事实，属于重复原文，不选。
D：文章只讨论杰弗瑞松树存在时期的那段干旱，至于有没有近期的干旱和文章无关，不选。