题目选项分析

Fossilized remains of a horn thought to be of a triceratops found in sedimentary rock in 2011

have been dated as being 65.5 million years old and thus

evidence that dinosaurs existed shortly before the asteroid impact that is believed to have made them extinct.

Fossilized remains of a horn thought to be of a triceratops found in sedimentary rock in 2011

have been dated at 65.5 million years old and thus are

evidence that dinosaurs existed shortly before the asteroid impact that is believed to have made them extinct.

题目基本信息

难度：难