4. The number of real roots of the equation $\sin x=\lg x$ is
A. 1
B. 2
C. 3
D. Greater than 3
Answer
As shown in the figure, when $x>10$, the graphs of $y=\sin x$ and $y=\lg x$ no longer intersect. Therefore, the number of intersection points between the graphs of $y=\sin x$ and $y=\lg x$ is 3. So the answer is $C$.