tpo9COLONIZING THE AMERICAS VIA THE NORTHWEST COAST 第一题为什么不能

考题你没贴出,下面我为你贴了：
1.According to paragraph 1,the theory that people first migrated to the
Americas by way of an ice-free corridor was seriously called into question by
A.paleoecologist Glen MacDonald's argument that the original migration occurred much later than had previously been believed
B.the demonstration that certain previously accepted radiocarbon dates were incorrect
C.evidence that the continental ice began its final retreat much later than had previously been believed
D.research showing that the ice-free corridor was not as long-lasting as had been widely assumed
答案是B .
关键句子是文章里的这一段：
But belief in this ice-free corridor began to crumble when paleonecologist Glen
MacDonald demonstrated that some of the most important radiocarbon dates used to support the existence of an ice-free corridor were incorrect.He persuasively argued that such an ice-free corridor did not exist until much later,when the continental ice began its final retreat.
从这些句子可以看到
the theory was called into question （理论被质疑）
的直接原因是 Glen MacDonald demonstrated that some of the most important radiocarbon dates used to support the existence of an ice-free corridor were incorrect.
即选项B .