[单选题]
The wave equation for hy -4.ij w 0cct g;ylo3n2r9kjuzdrogen has solutions only if the r:zfk: y-oqa1three quantum 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.