6. When $0<x<1$, the size relationship of $\frac{\sin x}{x},\left(\frac{\sin x}{x}\right)^{2}, \frac{\sin x^{2}}{x^{2}}$ is ( ).
(A) $\frac{\sin x}{x}<\left(\frac{\sin x}{x}\right)^{2}<\frac{\sin x^{2}}{x^{2}}$
(B) $\left(\frac{\sin x}{x}\right)^{2}<\frac{\sin x}{x}<\frac{\sin x^{2}}{x^{2}}$
(C) $\frac{\sin x^{2}}{x^{2}}<\frac{\sin x}{x}<\left(\frac{\sin x}{x}\right)^{2}$
(D) $\frac{\sin x^{2}}{x^{2}}<\left(\frac{\sin x}{x}\right)^{2}<\frac{\sin x}{x}$
6. (B).
$0B D=\operatorname{tg} x^{2}>x^{2}, \\
\therefore \frac{\sin x}{\sin x^{2}}<\frac{x-x^{2}}{x^{2}}+1=\frac{x}{x^{2}}, \\
\text { hence } \frac{\sin x}{x}<\frac{\sin x^{2}}{x^{2}} .
\end{array}
$$

It is clear that $\left(\frac{\sin x}{x}\right)=\frac{\sin x}{x}<\frac{\sin x^{2}}{x^{2}}$ holds.