【单选题】What is the origin of a magnetic field?
【单选题】A magnetic field exerts a force on a charged particle:
A.
if the particle is moving along the field lines
B.
if the particle is moving across the field lines
【单选题】During the transition of the Earth's magnetic field ______.
A.
the compass will become useless
B.
man and animals will be confused as to directions
C.
the magnetic strength of the Earth will disappear
D.
the magnetic strength of the Earth will be stronger
【单选题】A moving wire in the presence of a magnetic field has a _________ induced in it.
【单选题】A current-carrying wire in the presence of a magnetic field has a _________ induced on it.
【单选题】下列关于城域网特征的描述中,错误的是( )。
A.
城域网是介于广域网与局域网之间的一种高速网络
B.
城域网可满足几十公里范围内多个局域网互联的需求
C.
城域网可实现大量用户之间的数据、语音、图形与视频等多种信息的传输
【单选题】下列几种关于有机磷农药中毒的症状描述中,正确的是( )
【单选题】If a magnetic compass is not affected by any magnetic field other than the Earth’s which statement is TRUE?______.
A.
Compass error and variation are equal
B.
Compass north will be true north
C.
Variation will equal deviation
D.
There will be no compass error
【单选题】有丝分裂期 M 期可顺序分成 4 个阶段,下列顺序正确的是