6. Among 6 products, there are 4 genuine items and 2 defective items. Now, each time 1 item is taken out for inspection (the inspected item is not put back), until both defective items are found. What is the probability that both defective items are found exactly after 4 inspections?
(A) $\frac{1}{15}$
(B) $\frac{2}{15}$
(C) $\frac{1}{5}$
(D) $\frac{4}{15}$
6. C.

The required probability is
$$
\begin{array}{l}
\frac{2}{6} \times \frac{4}{5} \times \frac{3}{4} \times \frac{1}{3}+\frac{4}{6} \times \frac{2}{5} \times \frac{3}{4} \times \frac{1}{3}+ \\
\frac{4}{6} \times \frac{3}{5} \times \frac{2}{4} \times \frac{1}{3}=\frac{1}{5} .
\end{array}
$$