__________ some medals came to live in the sea is not known.

__________ some medals came to live in the sea is not known.
A、Which
B、Since
C、Although
D、How
【正确答案】：D
【题目解析】：该句的从句由疑问副词how引导的主语从句。选项B、C中的since和a1though不能引导主语从句；选项A中的which虽能引导主语从句，但与some矛盾。