为了让我们更好的适应sat考试，sat官网每天都会有sat官方每日一题，下面是小编为您整理的2016年4月sat官方每日一题，是阅读选择，让我们一起来看一看这道阅读选择吧。

　　Four billion years ago, Earth's continents began taking shape. Scientists long held that this process unfolded gradually. It would have taken millions of years for granite, the primary component of the continental crust, to form in the mantle and migrate to the upper crust, they reasoned. But new research suggests that these events may have proceeded at rather a different pace. According to a report published in the journal Nature, the emergence of granite occurred by way of swift, dynamic and possibly catastrophic events lasting from 1,000 to 100,000 years.

　　Geologist Alexander Cruden of the University of Toronto and his colleagues turned to experimental studies—melting rock samples, for example—to explore how granite magma forms and how fast it can move. Their results proved surprising. "In the past we thought that granite magma, which cools and crystallizes to form very large granite intrusions, moved up through kilometers of crust as large, solid blobs at rates of about a meter per year," Cruden says. "But we've found that magma actually has quite low viscosity and is relatively runny. Because it is runny, it is able to channel its way from the mantle and lower crust through fractures and cracks that are as small as one meter thick."

　　According to this model, granite intrusions in Greenland or the Canadian Shield, depending on their size, would have taken only thousands of years to form, which is extraordinarily fast from a geological point of view, Cruden notes.

　　The underlined word "unfolded" most nearly means ______________

　　(A) revealed.

　　(B) spread.

　　(C) developed.

　　(D) expanded.

　　答案：C

　　解析：

　　Choice C is the best answer. The author states that scientists have long believed that the formation of Earth's continents was a process that "unfolded gradually" over "millions of years." In this context, "unfolded" most nearly means" developed," or grew or advanced. The author means that the process advanced slowly over time.

　　上面是小编为您整理的2016年4月sat官方每日一题，是阅读选择题，为了让我们更好的适应sat考试，sat官网每天都会发布sat官方每日一题，让我们一起来看一看这道阅读选择吧。

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