5. Given that $x, y, z$ are 3 non-negative real numbers, and satisfy $3x + 2y + z = 5, x + y - z = 2$. If $s = 2x + y - z$, then the sum of the maximum and minimum values of $s$ is ( ).
(A) 5
(B) $\frac{23}{4}$
(C) $\frac{27}{4}$
(D) $\frac{35}{4}$
5.(A).

From $\left\{\begin{array}{l}3 x+2 y+z=5, \\ x+y-z=2, \\ 2 x+y-z=s\end{array}\right.$ we get $\left\{\begin{array}{l}x=s-2 \geqslant 0, \\ y=5-\frac{4}{3} s \geqslant 0, \\ z=1-\frac{1}{3} s \geqslant 0 .\end{array}\right.$
Then $2 \leqslant s \leqslant 3, s_{\text {max }}+s_{\text {min }}=5$.