10. Figure 4 shows the number of students who participated in football training each day last week. After calculating the mean and median, the coach found that actually 21 students attended the training on Wednesday. Which of the following correctly describes the change in the mean and median? 
(A) The mean increased by 1, and the median did not change
(B) The mean increased by 1, and the median also increased by 1
(C) The mean increased by 1, and the median increased by 5
(D) The mean increased by 5, and the median increased by 1
(E) The mean increased by 5, and the median also increased by 5
10. B.

Since the actual number of people on Wednesday is 5 more than the initially recorded number, the average has increased by $\frac{5}{5}=1$ person.

For the median, the initially recorded numbers of people are $16, 16, 20, 22, 26$. After correction, the numbers become $16, 20, 21, 22, 26$. The median changes from 20 to 21, so the median also increases by 1.