4. $1 \times 3 \times 5 \times 7 \times \cdots \times 1997 \times 1999 \times 2001 \times 2003 \times 2005$ The last three digits are $(\quad)$
A. 125
B. 375
C. 625
D. 875
4. B Hint: $(2 k+1) \cdot(2 k+3) \cdot(2 k+5) \cdot(2 k+7) \equiv 1(\bmod 8)$,
$$
\text { so } \begin{aligned}
2005!! & \equiv 1 \times 3 \times 5(\bmod 8) \\
& \equiv 7(\bmod 8) .
\end{aligned}
$$

and $125 \equiv 5(\bmod 8), 375 \equiv 7(\bmod 8)$
$$
625 \equiv 1(\bmod 8), 875 \equiv 3(\bmod 8)
$$