1. Given points $A(2,3)$, $B(5,4)$, $C(-4,1)$, connecting these three points in sequence. Then these three points ( ).
(A) form an equilateral triangle
(B) form a right triangle
(C) form an acute triangle
(D) lie on the same straight line
一、1. D.
It is easy to know that the equation of line $AB$ is $y=\frac{1}{3} x+\frac{7}{3}$. When $x=-4$, $y=1$.
Therefore, point $C$ lies on line $AB$.