Very Hot Stars Have Weak Hydrogen Spectral Lines

Multiple Choice

Very hot stars have weak hydrogen spectral lines. Why is this?

A) These stars contain very little hydrogen.
B) The hydrogen in the atmospheres of these stars is combined into molecules, and these have different spectra.
C) The electrons in the hydrogen atoms in these stars are all in their lowest energy levels, and they cannot radiate from these levels.
D) The hydrogen atoms in these stars are mostly ionized and hence cannot radiate.