17. Given a quadrilateral whose vertices lie on the graph of the function $y=\ln x$, the x-coordinates of these vertices are four consecutive positive integers, and the area of the quadrilateral is $S=\ln \frac{91}{90}$. Then the x-coordinate of the leftmost vertex is ( ).
(A)6
(B) 7
(C) 10
(D) 12
(E) 13
17. D.

As shown in Figure 8, let the coordinates of the four vertices of the quadrilateral be
$$
\begin{array}{l}
B(n, \ln n), \\
C(n+1, \ln (n+1)), \\
D(n+2, \ln (n+2)), \\
E(n+3, \ln (n+3)) .
\end{array}
$$
$=\frac{\ln n+\ln (n+1)}{2}+\frac{\ln (n+1)+\ln (n+2)}{2}+$ $\frac{\ln (n+2)+\ln (n+3)}{2}-3 \times \frac{\ln n+\ln (n+3)}{2}$ $=\ln \frac{(n+1)(n+2)}{n(n+3)}=\ln \frac{91}{90}$
$$
\Rightarrow n^{2}+3 n-180=0
$$
$\Rightarrow n=12$ or -15 (discard).

