7. In the quadratic equation $x^{2}+m x+n=0$, the coefficients $m, n$ can take values from $1,2,3,4,5,6$. Then, among the different equations obtained, the number of equations with real roots is ( ).
(A) 20
(B) 19
(C) 16
(D) 10
7.B.
$\Delta=m^{2}-4 n \geqslant 0$, then $m^{2} \geqslant 4 n$. When $n=1$, $m=2,3,4,5,6$, a total of 5; when $n=2$, $m=3,4,5,6$, a total of 4; when $n=3$, $m=4,5,6$, a total of 3; when $n=4$, $m=4,5,6$, a total of 3; when $n=5$, $m=5,6$, a total of 2; when $n=6$, $m=5,6$, a total of 2. In total, 19.