我的祖先几百年前从非洲来到了这里。

My ___ancestors came here from Africa centuries ago.

这种老式打字机是现代计算机的祖先之一。

This old typewriter is one of the ___ancestors of modern computers.

这种古代鱼类被认为是现代哺乳动物的祖先。

This ancient fish is considered an ___ancestor of modern mammals.