The great scientist became world-known in the early 1970s,______ he and another

题型：不详难度：来源：

The great scientist became world-known in the early 1970s,______ he and another scientist made new discoveries about black holes.

A．which

B．where

C．when

D．then

答案

C

解析

考查定语从句。先行词是时间，引导词在从句中作时间状语。