“How was ______ they discovered the entrance to the underground palace?” “Totally by chance.”

A．it that

B．he that

C．it when

D．he which

采用三B格式编程时加工指令为SR2时，表示（）。

A、圆弧的起点落在第二象限的顺时针圆弧

B、圆弧的起点落在第二象限的逆时针圆弧

C、圆弧的终点落在第二象限的顺时针圆弧

D、圆弧的终点落在第二象限的逆时针圆弧