The element radium, in the chemistry lab, gave off a blue light.
A. discovering
B. to be discovered
C. to discover
D. discovered
网友回答
A. discovering
B. to be discovered
C. to discover
(答案→)D. discovered
解析：考查过去分词作定语，此题表示被动完成，句意：在化学实验室被发现的镭元素释放出蓝色的光。故选D。