某对称水闸宽度方向水平尺寸基准的位置是什么?
What is the horizontal dimension benchmark at a width direction for a symmetric sluice？
A、水闸对称轴线the axis of symmetry of sluice
B、闸门槽处the sluice gate slot
C、水闸起始端The starting point of sluice
D、水闸尾端The end of sluice