7.若离散型随机变量X∼B(n,23)X\sim B({n,\frac{2}{3}})X∼B(n,32),且D(X)=89D(X)=\frac{8}{9}D(X)=98,则P(X⩽2)=(P(X\leqslant 2)=(P(X⩽2)=( )))