$10 \cdot 52 \quad 1990-1980+1970-1960+\cdots-20+10$ equals
(A) -990 .
(B) -10 .
(C) 990 .
(D) 1000 .
(E) 1990 .
(6th American Junior High School Mathematics Examination, 1990)
［Solution］It is only necessary to notice that
$$
\begin{aligned}
\text { Original expression } & =(1990-1980)+(1970-1960)+\cdots+(30-20)+10 \\
& =99 \cdot 10+10=1000 .
\end{aligned}
$$

Therefore, the correct choice is $(D)$.