8. For any $\triangle A B C$, let its perimeter, circumradius, and inradius be $l, R$, and $r$, respectively, then
A. $l>R+r$
B. $l \leqslant R+r$
C. $\frac{l}{6}<R+r<6 l$
D. $\mathrm{A} 、 \mathrm{~B} 、 \mathrm{C}$ three relationships are all incorrect
When $\triangle A B C$ is an equilateral triangle, $R+r=\frac{\sqrt{3} l}{6}<l$, eliminating $B$; when $A \rightarrow \pi, B, C \rightarrow 0$, $2 R=\frac{a+b+c}{\sin A+\sin B+\sin C} \rightarrow+\infty$, eliminating $A, C$. Therefore, the answer is $D$.