2.11 people jointly manage an arsenal, and some locks are added to the door, and each person is given several keys. To ensure that any 6 people together can open all the locks, but any 5 people together cannot open all the locks, how many locks should be installed on the door at least? How should the keys be distributed?
（Hint 8
Use Example 3. The answer is: at least $C_{11}^{5}$ attempts).