请老师解释下c d e的区别 我错选了c

请老师解释下c d e的区别 我错选了c

C和E的区别

选了A主语是rock samples，谓语我就随便猜了一个猜的单数，因为在非划线部分没有看到有提示这个词是单数还是复数的地方，还有后面那个为什么是dated at 3.47而不是dated to be 3.47

在复习中我感觉较有难度的是对SC语意精准地理解及辨别选项的细微差别造成的语意区别。常见的问题有以下两大类： 1． 两个选项的差别只有某个介词时，我会觉得难以定度。就算我理解原句作者想表达的意思，但是对于选用哪个介词能更精确地表达句意还是不太拿捏得准。 以下是该情况的例子之一 (ID: 1736)（括号代表画线处） Rock samples taken from the remains of an asteroid about twice the size of the 6-mile-wide asteroid that eradicated the dinosaurs （has been dated at 3.47 billion years old and thus is） evidence of the earliest known asteroid impact on Earth. A. has been dated at 3.47 billion years old and thus is B. has been dated at 3.47 billion years old and thus C. have been dated to be 3.47 billion years old and thus are D. have been dated as being 3.47 billion years old and thus E. have been dated at 3.47 billion years old and thus are 我做此题时觉得CE差别不大，对于这种语意精确度的敏感性该如何训练？ (另：感觉这种考题在GMAT 考试中有增多趋势，故不能随便蒙一个答案) 2． 两个事物作比较用than 连接时，较容易头晕。因为此时对画线的第二个比较对象给出的选项中有省代词的，有省动词的，还有都省的……; 然后我就会觉得比到最后好像剩下的两个都还可以。 以下是该情况的例子之一 (ID: 1363) Accordingly to public health official, in 1998 Massachusetts became the first state in which more babies were born to women over the age of thirty （than） under it. A. than B. than born C. than they were D. than there had been E. than had been born 我觉得AC 都还凑合，而A 省得太多了。 请问针对以上情况该如何进行训练？ 谢谢！