A harmonious society is like a symphony or orchestra — each person contributes a small sound, but when （）with other sounds, it becomes beautiful music.
A、
combining
B、
being combined
C、
combined
D、
to be combined
【正确答案】：C
【题目解析】：
由but后面的句子可知，when引导的从句的主语是it，it与combine为被动关系，故用过去分词形式。