骶骨前后位摄影的中心线是 ["A.垂直投射","B.向头侧倾斜15°","C.向足侧倾斜15°","D.向头侧倾斜45°","E.向足侧倾斜45°"]
第3~7颈椎前后位摄影时,中心线应 ["A.向头侧倾斜20° ","B.向头侧倾斜10° ","C.垂直入射胶片 ","D.向足侧倾斜10° ","E.向足侧倾斜20°"]
()使不同区域中海水主要化学成分含量的差别减小到最低程度,因而其含量具有相对稳定性。
关于前臂侧位摄影,错误的叙述是 ["A.尺侧靠近暗盒","B.桡侧靠近暗盒","C.肘部屈曲约90°","D.肩部尽量放低","E.掌面垂直暗盒"]
全阴天是指云量占整个天空面积的()的天气。 ["A、20%","B、50%","C、80%","D、100%"]
海水盐度=()