单项选择题

Questions 49 to 52 are based on the following passage: 　　One of the earliest and most influential proponents of the idea of continental drift was a German astronomer, meteorologist, and explorer named Alfred Wegener.In 1912 he advanced good arguments to support the idea that at one time there was no Atlantic Ocean. The Americas and Greenland were welded with Europe, Africa, Australia and Antarctica into one large continent, Pangaea. 　　His strongest argument seemed to be the remarkable similarity of the continental margins on opposite sides of the Atlantic. But he also looked at similarities in ancient geologic structures, fossil records, and ancient climates to support his hypothesis. He pointed out that some unique geological structures in the Americas terminate abruptly in the Atlantic Ocean and then continue again on the other side of the Atlantic, as if the structures had formed when the continents were together and then were cleaved as the continents tore apart. He showed that the fossil records on both sides of the Atlantic were similar up to about a hundred million years ago and then showed divergence, indicating that the continents had become isolated from each other at that time. Finally, by using fossils and sediments, he was able to demonstrate that ancient climates on both sides of the Atlantic were similar,although they were quite different from those presently found in the respective regions. 　　Wegener’s interesting ideas were too revolutionary to be easily accepted or seriously considered at the time. He died in 1930, more than two decades before further evidence forced reconsideration and eventual acceptance of his revolutionary way of looking at our world. Wegener’s ideas about continental drift are properly termed a "hypothesis" (line9) because