My sister is waiting for me at the next stop, ____ I have to get

My sister is waiting for me at the next stop, ____ I have to get off there.
A、and
B、so
C、since
D、when
【正确答案】：B
【题目解析】：考察连词，句子前后为因果关系，因为妹妹在等我，所以我必须在这里下车。