I think I was at school,      I was staying with a friend during the vacation when Iheard the news.[      ]

A. even so      

B. and then      

C. or else      

D. so that

点火系电路有故障时，用中央高压线做跳火试验有火，用高压分线做跳火试验无火，则表明（）有故障。

A、高压电路

B、低压电路

C、点火开关

D、启动开关