$6 \cdot 35$ If $\lg 3=0.47712$, then which of the following four logarithmic values is incorrect?
(A) $\lg 1.5=0.17609$.
(B) $\lg 5=0.69897$.
(C) $\lg 2=0.30103$.
(D) $\lg 7=0.84519$.
(1st "Hope Cup" National Mathematics Invitational, 1991)
[Solution] If $(A)$ is wrong, then by $\lg 1.5=\lg 3-\lg 2$, that is,
$$
\lg 2=\lg 3-\lg 1.5=0.47712-0.17609=0.30103,
$$

we know that $(C)$ is also wrong, which contradicts the problem statement. Therefore, $(A)$ and $(C)$ are both true.
Also, $\lg 2+\lg 5=0.30103+0.69897=1$, and since $(C)$ is true, $(B)$ is also true.
$\therefore$ Only $(D)$ is wrong.
Thus, the answer is $(D)$.