7. There are 5 pairs of shoes with different sizes. If 4 shoes are taken out, the probability of getting exactly one pair is $\qquad$ .
$\begin{array}{l}\text { II.7. } \frac{4}{7} . \\ P=\frac{\mathrm{C}_{5}^{1} \mathrm{C}_{4}^{2} \mathrm{C}_{2}^{1} \mathrm{C}_{2}^{1}}{\mathrm{C}_{10}^{4}}=\frac{120}{210}=\frac{4}{7} .\end{array}$