为使汽车发动机能在各种困难条件下点火起动，要求作用于火花塞两电极间的电压至少在7000～8000V。
参考答案：对
________ you have to do the job, you should try your best to do it well even though it may be very difficult for you.
A．Since
B．While
C．Unless
D．Though
结构化程序设计包含3种基本控制结构，其中SCAN-ENDSCAN语句属于【 】结构。
