5. Figure 1 is a simplified model of a traffic roundabout at a three-way intersection. During a certain peak period, the number of motor vehicles entering and exiting intersections $A, B$, and $C$ per unit time is shown in Figure 1. The $x_{1}, x_{2}$, and $x_{3}$ in the figure represent the number of motor vehicles passing through the road segments $\overparen{A B}$, $\overparen{B C}$, and $\overparen{C A}$ per unit time during this period (assuming that in the same road segment, the number of vehicles entering and exiting per unit time is equal). Then $(\quad)$.
(A) $x_{1}>x_{2}>x_{3}$
(B) $x_{1}>x_{3}>x_{2}$
(C) $x_{2}>x_{3}>x_{1}$
(D) $x_{3}>x_{2}>x_{1}$
5.C.

According to the problem, we have $x_{1}=50+x_{3}-55=x_{3}-5$, so $x_{1}<x_{3}$. Similarly, $x_{1}<x_{2}, x_{3}<x_{2}$.