7. The number of positive integers $n$ that make $\frac{n}{30-n}$ a positive integer is $(\quad)$.
(A) 4
(B) 5
(C) 6
(D) 7
(E) 8
7. D.

Notice,
$$
\frac{n}{30-n}=\frac{n-30+30}{30-n}=\frac{30}{30-n}-1
$$

is a positive integer.
Therefore, $(30-n) \mid 30$.
Hence, $30-n=1,2,3,5,6,10,15$.
Thus, $n=29,28,27,25,24,20,15$, a total of seven.