问题
填空题
People used to think that there is no grass before the extinction of dinosaurs.
答案
参考答案：Y
解析：通过阅读文章可以发现在第一个小标题下的第三段中有Caroline说的一句话：…until now“it has been assumed that dinosaurs lived in virtually grass-free ecosystems．”。也就是说在以前人们都认为那个时候是没有植物的。