the injured boy must be sent to the hospital at once,()his relatives called the police for help

题目

the injured boy must be sent to the hospital at once,()his relatives called the police for help
A or B so C but D and
请问为什么不是C……

答案

the injured boy must be sent to the hospital at once,(B)his relatives called the police for help
A or B so C but D and
请问为什么不是C……
答案解析：答案为B ,前面句子说的原因,后面句子说的结果,用并列连词SO 表示结果,