“化石的”用英语怎么说

科学家根据那些化石的骨骼结构确定其年代.Scientists have dated the fossils by their bone structure.有两个因素对生物化石的保存是有利的.Tow factors are favorable for the preservation of organisms as fossils.它们是怎样变成化石的?How did they become fossils?...