was not until the early 20th century the importance of his ideas was realized.
A. What; that
B. It; that
C. That; so
D. It ;when
网友回答
A. What; that
(答案→)B. It; that
C. That; so
D. It ;when
解析：考查强调句的特殊句型：It was not until….that….，直到…才…，句意：直到20世纪初，他思想的重要性才被意识到。选B。