单项选择题
The magnetic compass operates on the principle that（）.
A.like magnetic poles attract B.unlike magnetic poles repel C.unlike poles attract D.the poles of the compass line up with the geographic poles of the earth
单项选择题 The magnetic compass magnets are acted on by the horizontal component of the Earth’s total magnetic force. This magnetic force is GREATEST at the（）.
单项选择题 The lubber’s line on a magnetic compass indicates（）.
单项选择题 The lubber’s line of a magnetic compass（）.
