自2013年12月考次起，全国大学英语四、六级考试委员会将对四、六级考试的试卷结构和测试题型作局部调整。快来一睹四六级新题型的风采吧~
You can tell the age of a tree by counting its rings, but these records of a tree's life really say a lot more. Scientists are using tree rings to learn what's being happening on the sun's surface for the last ten thousand years. Each ring represents a year of growth. As the tree grows, it adds a layer to its trunk taking up chemical elements from the air. By looking up the elements in the rings for a given year, scientists can tell what elements were in the air that year. Doctor Stevenson is analyzing one element —— carbon-14 in ring from both living and dead trees. Some of the rings go back almost ten thousand years to the end of the Ice Age.