【单选题】
两相干波的波动方程分别为:<img src="https://nimg.ppkao.com/2018-09/wangjing/2018092816281557244.jpg?sign=221206f589f886b6951016307682a933&t=62d1ab7b" />,由A,B两点无衰减的相向传播,AB=2λ,则A、B连线中点处振幅为:()<img src="https://nimg.ppkao.com/2018-09/wangjing/2018092816283750150.jpg?sign=053bccbb17cd1990421be751af075bf7&t=62d1ab7b" />
A、A
B、B
C、C
D、D