【判断题】各 国的移民管理机关主要 依靠口岸现场 的 执法 人 员证件 查验、观察、询问 等 手段, 发 现和查获不准入出境人员 。( )
【单选题】某站水准测量时,由A点向B点进行测量,已知A点的高程为251m,测得后视读数为a=1.000m,前视读数为b=2.283m,则视线高Hi和待测点B的高程分别为
【单选题】Using a pulse-echo technique, if the major plane of a flat discontinuity is oriented at some angle other than perpendicular to the direction of sound propagation, the result may be()
A.
Loss of signal linearity
B.
Loss or lack of a received discontinuity echo
C.
Focusing of the sound beam
D.
Loss of interference phenomena