7. There are 52 playing cards, with 13 cards of each of the 4 suits: hearts, diamonds, clubs, and spades. If 2 cards are drawn at random, the probability that they are of the same suit is ( ).
A. $\frac{1}{16}$
B. $\frac{1}{13}$
C. $\frac{1}{12}$
D. $\frac{4}{17}$
E. $\frac{1}{4}$
$\mathrm{D}$