Overhead railway, whose tracks are elevated out of the way of surface traffic, ______one possible solution to heavy traffic in big cities. A．might be B．might have been C．have been D．should have been
A. A．might B.might C.have D.should
【参考答案】
A 本题考查情态动词的用法，题意为，轨道被提高、远离地面交通的高架铁路，可能是(解决)大城市交通堵塞的一个可行办......