【单选题】The spectacular auroral light displays that appear in Earth's atmosphere around the north and south magnetic poles were once mysterious phenomena. Now, scientists have data from satellites and ground-...
A.
The periodic variation in the displays of auroras.
B.
The information and appearance of auroras around the Earth's poles.
C.
The factors that cause the variety of colors in auroras.
D.
The methods used to observe auroras from outer space.