Ans: B
$\begin{array}{cl}
& \left(\dfrac{1}{2}\right)^{888} (-2)^{887} \\
= & (2^{-1})^{888} \times (-1)^{887} \times 2^{887} \\
= & -1 \times 2^{-888} \times 2^{887} \\
= & -1 \times 2^{-888+887} \\
= & -1 \times 2^{-1} \\
= & -0.5
\end{array}$
$\begin{array}{cl}
& \left(\dfrac{1}{2}\right)^{888} (-2)^{887} \\
= & (2^{-1})^{888} \times (-1)^{887} \times 2^{887} \\
= & -1 \times 2^{-888} \times 2^{887} \\
= & -1 \times 2^{-888+887} \\
= & -1 \times 2^{-1} \\
= & -0.5
\end{array}$
