23. 已知a2−2ab−3b2=1a^{2}-2ab-3b^{2}=1a2−2ab−3b2=1,且−1⩽log2(a+b)⩽1-1\leqslant \log _{2}(a+b)\leqslant 1−1⩽log2(a+b)⩽1,则a−ba-ba−b的取值范围是((( )))