A.20 B.30 C.40 D.50
A.18.72m B.16.72m C.18.61m D.16.61m
A.兩個已知點(diǎn)上 B.一個已知點(diǎn)高,一個已知點(diǎn)低 C.兩個已知點(diǎn)和它們的連線上 D.兩個已知點(diǎn)連線的精度