[单选] Although the main business of the shipowners may be that of brewers，in their capacity as shipowners they must（）by the standard of conduct of the ordinary reasonable Shipowner in the management and control of vessels.

目前微机使用的软盘直径为（），容量为1.44M。 3.5厘米。 12厘米。 3.5英寸。 12英寸。 试比较PS1和PS2的结构及功能特点。 静止液体中同一水平面上各点的压强（）。 都相等。 都不一样。 不完全相等。 可能相等。 If the pump for a hydraulic anchor windlass is overheating, the cause may be （）. excessive drive motor speed。 excessive pump discharge pressure。 too low of a tilting box angle。 insufficient drive motor speed。 输送聚合物母液，选择螺杆泵，其主要原因是（） 螺杆泵工作平稳。 有自吸能力。 成本较低。 防止粘度损失。 Although the main business of the shipowners may be that of brewers，in their capacity as shipowners they must（）by the standard of conduct of the ordinary reasonable Shipowner in the management and control of vessels.