1. The number of rational numbers $x$ that satisfy the equation
$$
|x-1|-2|x-2|+3|x-3|=4
$$
is ( ) .
(A) 1
(B) 2
(C) 3
(D) infinitely many
-.1.D.
Points $1,2,3$ divide the number line into four intervals:
$$
(-\infty, 1],(1,2],(2,3],(3,+\infty) \text {. }
$$

Under these conditions, removing the absolute value symbol yields the solutions $1 \leqslant x \leqslant 2, x=5$, which include infinitely many rational numbers.