用经纬仪进行视距与高差测量时,在 A 点上架设经纬仪,在 B 点上立视距尺,观测得上、中、下丝的读数分别为 3.578m 、 3.000m 与 2.422m ,竖直角为 -3°29′20′′ ,仪器高度 1.42m 。问 AB 两点间的平距 m ,高差 m ,若 A 点的高程为 H A = 30.00 , B 点的高程 H B = m 。
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举一反三
【单选题】The author brings her children to visit a nursing home and __________ .
A.
this is the first time the children pay such a visit
B.
this is one of the rare visits there by the children
C.
this is one of the many visits there by the children