6 Among all lines passing through the point $(\sqrt{3}, 0)$, the number of lines that pass through two different rational points is ( )
A. 0
B. infinitely many
C. at least two
D. only one
6 D. Obviously, $x=\sqrt{3}$ does not meet the requirement.
Suppose the equation of the line is $y=k(x-\sqrt{3})$, and it passes through rational points $P_{1}\left(x_{1}, y_{1}\right), P_{2}\left(x_{2}, y_{2}\right)$, then $k=\frac{y_{2}-y_{1}}{x_{2}-x_{1}}$ is a rational number. Also, $y_{1}=k\left(x_{1}-\sqrt{3}\right)$. By comparing the irrational parts, we get $k=0$. Therefore, the line that meets the condition is only one, which is the $x$-axis.