【单选题】
在水准测量一个测站上，已知后视点A的高程为856.458，测得后视点A的读数为1.320，则可求得该测站仪器的视线高为（ ）。
①
857.778
②
-857.778
③
855.138
④
-855.138
【单选题】
A点坐标为（10、20、30），B点坐标为（30、20、30）则AB距离为______。
①
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