The public transportation is very convenient in that big city , so there______be any difficulty in

traveling around .

A．mustn’t

B．wouldn’t

C．shouldn’t

D．needn’t

无热膨胀管道的吊架，其吊杆应（）安装。

A、向水流方向倾斜15°

B、水平

C、垂直

D、向水流相反方向倾斜15°