A beam of electrons bombards a sample of hydrogen.Through what potential difference must the electrons have been accelerated if the first line of the Balmer series is to be emitted？（）

A beam of electrons bombards a sample of hydrogen.Through what potential difference must the electrons have been accelerated if the first line of the Balmer series is to be emitted？（）
A.569.3 V
B.35.7 V
C.0.6 V
D.12.1 V
正确答案：12.1 V