22. Tom's algebra notebook has a total of 50 pages, 25 sheets, where the 1st and 2nd pages are the front and back of the 1st sheet, the 3rd and 4th pages are the front and back of the 2nd sheet, and so on. One day, Tom left the notebook on the table when he went out, and his roommate took several consecutive pages from the notebook. The average of the remaining page numbers is 19. How many sheets did the roommate take? 
(A) 10
(B) 13
(C) 15
(D) 17
(E) 20
22. B.

Let the notes taken by the roommate be from page $2 a-1$ to page $2 b$. Then
$$
\begin{array}{l}
\frac{(2 a-1+2 b)(2 b-2 a+2)}{2}+ \\
19 \times(50-(2 b-2 a+2))=\frac{50 \times 51}{2} \\
\Rightarrow(2 a+2 b-39)(b-a+1)=25 \times 13 \\
\Rightarrow(2 a+2 b-39, b-a+1) \\
\quad=(25,13) \text { or }(13,25) .
\end{array}
$$

If $b-a+1=25$, then
$$
b \geqslant 25 \Rightarrow 2 b \geqslant 50 \text {, }
$$

which does not meet the problem's conditions (discard).
$$
\text { Therefore, }\left\{\begin{array} { l } 
{ b - a = 1 2 , } \\
{ a + b = 3 2 }
\end{array} \Rightarrow \left\{\begin{array}{l}
a=10, \\
b=22 .
\end{array}\right.\right.
$$

Thus, the answer is $\frac{2 b-2 a+1+1}{2}=13$.