手工下向焊的第一层焊道适合采用（）运条法。
A、直线形
B、锯齿形
C、月牙形
D、圆圈形
参考答案：A
Nancy, ____ for about half a year to apply for a job as an airline hostess, finally took a position at a shopping center.
A．struggled
B．having struggled
C．struggling
D．to struggle
求经过点A(2，m)和B(n，3)的直线方程．
