17. Calculate:
$$
\begin{array}{l}
\frac{1 \times 3}{2 \times 2} \cdot \frac{2 \times 4}{3 \times 3} \cdot \frac{3 \times 5}{4 \times 4} \cdots \cdots \frac{97 \times 99}{98 \times 98} \cdot \frac{98 \times 100}{99 \times 99} \\
=(\quad) .
\end{array}
$$
(A) $\frac{1}{2}$
(B) $\frac{50}{99}$
(C) $\frac{9800}{9801}$
(D) $\frac{100}{99}$
(E) 50
17. B.

The required expression is simplified as
$$
\frac{1}{2} \cdot \frac{3 \times 2}{2 \times 3} \cdot \frac{4 \times 3}{3 \times 4} \cdots \cdots \frac{99 \times 98}{98 \times 99} \cdot \frac{100}{99}=\frac{50}{99} .
$$