that these creatures are linked to a common ancestor.A. As is believedB. What is believed

问题补充：

that these creatures are linked to a common ancestor.

A. As is believed

B. What is believed

C. That is believed

D. It is believed

答案：

A. As is believed

B. What is believed

C. That is believed

(答案→)D. It is believed

解析：考查句型：It is believed that…，据相信…,it 是形式主语，that引导的是真正的主语，句意：据相信这些生物和一个共同的祖先有联系。选D。