4. If $B x \geqslant \sin x \geqslant A x (A, B$ are constants $)$ holds for $0 \leqslant x \leqslant \frac{\pi}{2}$, then the minimum value of the constant $B-A$ is $\qquad$; for any acute triangle $\triangle ABC$, it is always true that
$$
\sin A+\sin B+\sin C>M
$$

then the maximum value of $M$ is $\qquad$
4. $1-\frac{2}{\pi}, 2$