A:①④
B:③④
C:②③
D:①②
English, she went to school in London, England.
如图所示为氢原子能级示意图,现有大量的氢原子处于n=4的激发态,当向低能级跃迁时辐射出若干种不同频率的光,下列说法正确的是( )