6. In Rt $\triangle A B C$, $A B=3, A C=4, B C=5$. Now, let the distances from $A, B, C$ to a certain line $l$ be $d_{A}, d_{B}, d_{C}$ respectively. If $d_{A}: d_{B}: d_{C}=1: 2: 3$, then the number of lines $l$ that satisfy the condition is ( ) lines.
(A) 1
(B) 2
(C) 3
(D) 4
6. D.

Since the distances from $A, B, C$ to $l$ are all unequal, $l$ is not parallel to $AB$, $BC$, or $CA$. Consider the intersection points of $l$ with the sides (or their extensions) of the triangle. Given that $d_{A}: d_{B}=1: 2$, there are internal division points $X_{1}$ and external division points $X_{2}$ on $AB$ such that
$$
A X_{1}: X_{1} B=1: 2, X_{2} A: X_{2} B=1: 2 \text {. }
$$

Similarly, $l$ intersects $BC$ at two points $Y_{1}, Y_{2}$, and $l$ intersects $AC$ at two points $Z_{1}, Z_{2}$. Among these 6 points, there are 4 cases where three points are collinear, i.e., figure \& $\left(Y_{2}, X_{1}, Z_{1}\right),\left(Y_{2}, Z_{2}, X_{2}\right),\left(Y_{1}, X_{1}\right.$, $\left.Z_{2}\right),\left(Y_{1}, Z_{1}, X_{2}\right)$.