Years before the advent of plate tectonics―the widely accepted theory, developed in the mid-1960's, the holds that the major features of Earth's surface are created by the horizontal motions of Earth's outer shell, or lithosphere―a similar theory was rejected by the geological community. In 1912, Alfred Wegener proposed, in a widely debated theory that came to be called continental drift, that Earth's continents were mobile. To most geologists today, Wegener's The origin of Continents and Oceans appears an impressive and prescient document, containing several of the essential presumptions underlying plate tectonics theory: the horizontal mobility of pieces of Earth's crust; the essential difference between oceanic and continental crust; and a causal connection between horizontal displacements and the formation of mountain chains. Yet despite the considerable overlap between Wegener's concepts and the later widely embraced plate tectonics theory, and despite the fact that continental drift theory presented a possible solution to the problem of the origin of mountains at a time when existing explanations were seriously in doubt, in its day Wegener's theory was rejected by the vast majority of geologists. Most geologists and many historians today believe that Wegener's theory was rejected because of its lack of an adequate mechanical basis. Stephen Jay Gould, for example, argues that continental drift theory was rejected because it did not explain how continents could move through an apparently solid oceanic floor. However, as Anthony Hallam has pointed out, many scientific phenomena, such as the ice ages, have been accepted before they could be fully explained. The most likely cause for the rejection of continental drift―a cause that has been largely ignored because we consider Wegener's theory to have been validated by the theory of plate tectonics―is the nature of the evidence that was put forward to support it. Most of Wegener's evidence consisted of homologies―similarities of patterns and forms based on direct observations of rocks in the field, supported by the use of hammers, hand lenses, and field notebooks. In contrast, the data supporting plate tectonics were impressively geophysical―instrumental determinations of the physical properties of Earth garnered through the use of seismographs, magnetometers, and computers. 我选了E considerable overlap前面是despite XXX说明这个是个成就，他和后面的反对W的观点的事情是相反的。所以感觉D说用这个词的目的是解释为啥W理论。请老师辨析DE！谢谢！

请问这一题的解题思路

求问解题思路

求问解题思路

条件一：（30+⏹）（20+🔼）=864化简为20🔼-🔼^2=64 然后从2开始带入，得出当🔼=4时成立。条件二：⏹✖️🔼=24得出3、8和4、6两组可能解，分别带入，只有36和24成立，所以条件二充分。请问以上这个解题思路对吗，或者说有更简便的？

第14题 请徐老师解答 谢谢！

请问这道题的解题思路

第13题: 听老师jj课里讲的说选C，我不太明白条件2的分析，老师上课说条件2，若st同号，上式取等号，若st一正一负时，上式是小于号。那不就可以通过条件2直接判断上式大于号不成立吗，也就是答案是No。请老师更正下我的思路。

请徐老师讲下这两道题：这两个都做对了 但是感觉做的时候不太自信，想了一会，想听下老师的思路。谢谢老师！

麻烦徐老师讲一下Q9，选了E。我的思路是分析rounding后estimate的最大和最小的差值。

请徐老师讲一下Q7思路。读题是不是很明白题意说的到head的概率不是1/2。