8. For any real numbers $A, B, C$, the maximum value of the trigonometric expression $\sin ^{2} A \cos ^{2} B+\sin ^{2} B \cos ^{2} C+\sin ^{2} C \cos ^{2} A$ is
$\qquad$ .
8. 1 Detailed Explanation: $1=\left(\sin ^{2} A+\cos ^{2} A\right)\left(\sin ^{2} B+\cos ^{2} B\right)\left(\sin ^{2} C+\cos ^{2} C\right)=\sin ^{2} A \cos ^{2} B\left(\sin ^{2} C+\cos ^{2} C\right)+$ $\sin ^{2} B \cos ^{2} C\left(\sin ^{2} A+\cos ^{2} A\right)+\sin ^{2} C \cos ^{2} A\left(\sin ^{2} B+\cos ^{2} B\right)+\sin ^{2} A \sin ^{2} B \sin ^{2} C+\cos ^{2} A \cos ^{2} B \cos ^{2} C \geqslant$ original expression.