6. Let the set $T=\left\{x_{1}, x_{2}, \cdots, x_{10}\right\}$ have five-element subsets such that any two elements of $T$ appear in at most one subset. The maximum number of such subsets is $n$. Then $n$ equals ( ).
(A) 252
(B) 10
(C) 8
(D) 18
6. C.

An element has a chance to be in the same subset with 9 other elements, and the following is true for $S$ when $n \leqslant 4 \times 10, n \leqslant 8$.
Moreover, the sets $\left\{x_{1}, x_{2}, x_{3}, x_{4}, x_{5}\right\},\left\{x_{1}, x_{6}, x_{7}, x_{8}\right.$, $\left.x_{9}\right\},\left\{x_{1}, x_{3}, x_{5}, x_{6}, x_{8}\right\},\left\{x_{1}, x_{2}, x_{4}, x_{7}, x_{9}\right\},\left\{x_{2}, x_{3}\right.$, $\left.x_{8}, x_{7}, x_{10}\right\},\left\{x_{3}, x_{4}, x_{7}, x_{8}, x_{10}\right\},\left\{x_{4}, x_{5}, x_{8}, x_{9}, x_{10}\right\}$, $\left\{x_{2}, x_{5}, x_{6}, x_{9}, x_{10}\right\}$ are 8 subsets that meet the requirements.