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【单选题】用自准直法测量三棱镜顶角时，转动望远镜可测出两个方位角读数，这两个方位角读数之差是
A.
待测三棱镜顶角
B.
待测三棱镜顶角的补角
C.
待测三棱镜顶角的一半
D.
近似 180 度
【单选题】Subways are underground trains, which usually operate 24 hours a day. They are found in larger cities and usually run between the suburbs and the downtown area. Maps and schedules are available from t...
A.
within downtown areas
B.
away from city centers
C.
in or outside big modern cities
D.
between suburbs and city centers