曼哈顿一道SC题求大神解答~

FRACAS

Modern-day snakes are believed to evolve from four-legged lizards, but scientists were divided over whether that phase of evolution occurred on land or in the sea; the recent discovery of fossils of a land-dwelling snake with two legs provides new information for the ongoing debate.

• Aevolve from four-legged lizards, but scientists were
• Bhave evolved from four-legged lizards, but scientists are
• 为什么选B不选A呀....我个人理解是后面说了recent discovery所以前面的be divided over应该是发生在过去的事情啊...为什么要用are？是因为在阐述一件客观事实吗？
  

chasedream1999

现在我们看到的snake，物种进化已经（早都）完成了；科学家的意见主要有2种，只是最近又出土了新的证据来支持某一方，争论现在依然存在，留意句尾 provides new information for the ongoing debate，并不是结束了争论。

自己也是刚接触GMAT，正好也在看曼哈顿SC，大家一起讨论哈