求问一个tpo里的阅读句子找等价的题目 非常感谢

tpo45里一篇Microscopes The Beringia Landscape中的一道题：
6.Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

The presence of mammal species that require grassland vegetation has led Arctic biologist Dale Guthrie to argue that while cold and dry, there must have been broad areas of dense vegetation to support herds of mammoth, horse, and bison.

排除明显不合适的选项，我在cd两个里纠结了，正确是c，请问d选项错在哪里呢？我感觉d中最后破折号后部分代入整句意思不是很懂了
C. Dale Guthrie argued that Beringia, though cold and dry, must have had enough dense vegetation to support the herds of mammoth, horse, and bison that lived there.
D. As long as Beringia was cold and dry, argued Dale Guthrie, dense vegetation grew in order to support the herds of mammoth, horse, and bison—the mammal species present there.

谢谢～

原句的逻辑是虽然cold and dry，但是D项是只要cold and dry，马上就排除了

改写的是原句argue后面的内容，从句while cold and dry表转折，符合C项的though。As long as逻辑关系更像是因果或者条件。破折号后面是修饰mammoth, horse and bison，可以不用看。