Though having lived abroad for years, many Chinese still ______ the traditional customs. [ ]

A. perform

B. possess

C. observe

D. support

某测量小组对一工地采用经纬仪进行测量，经纬仪结构如图4-6所示。该测量小组对经纬仪照进行检校，将仪器粗平后，转动照准部使水准管平行于任意一对脚螺旋，调节该对脚螺旋使水准管气泡居中，转动照准部180°后，气泡偏离超过1格，故经纬仪的照准部水准管轴不垂直于竖轴，即LL不垂直于VV，因此需要检校。请写出经纬仪照准部水准管的校正过程。