6. In an oblique $\triangle A B C$, $a, b, c$ are the sides opposite to angles $A$, $B, C$ respectively, then the points $M(a, \sin A), N(b, \sin B)$, $P(c, \sin C)$ have the relationship $(\quad)$.
(A) The three points are collinear on $l$, and $l$ passes through the origin
(B) The three points are collinear on $l$, and $l$ does not pass through the origin
(C) Form $\triangle M N P$, and the origin is inside $\triangle M N P$
(D) Form $\triangle M N P$, and the origin is outside $\triangle A M N P$
6. (A)

By the Law of Sines, we have $\left\{\begin{array}{l}c=2 R \sin A, \\ b=2 R \sin B, \\ c=2 R \sin C .\end{array}\right.$ This indicates that points $M, N, P$ all lie on the line $l: y=2 R x$, and $l$ passes through the origin.