[单选题]
The wave equation for hydrogen has solutions only if the threkay8 j3tlk/c :e quantu +qhs2auc k-hm,rp1 0n l8ykn6m numbers $n$, $l$, and $m_l$ meet certain conditions. One of these conditions specifies that n
A. can be any real number.
B. can be any non-negative integer.
C. can be any integer.
D. can be any positive integer.
