$6 \cdot 58$ If the unit digit of $3^{1987}$ is $A$, the highest digit is $B$, and the number of integer digits is $C$ (given $\lg 3=0.47712$), then the value of $A+B+C$ is
(A) 965.
(B) 964.
(C) 962.
(D) None of the above answers is correct.
(China Beijing High School Mathematics Competition, 1987)
[Solution] From $\lg 3^{1987}=1987 \cdot \lg 3=1987 \cdot 0.47712=948.03744$.
Therefore, the number of integer digits of $3^{1987}$ is $C=949$.
Also, $3^{1987}=3^{4 \cdot 496+3}$, so the last digit of $3^{1987}$ is the same as the last digit of $3^{3}$, i.e.,
$$
A=7 \text {. }
$$

Since $\lg 3^{1987}=948.03744$, we can determine that the leading digit $B=1$.
$$
A+B+C=949+7+1=957 .
$$

Therefore, the answer is $(D)$.