2016 Beijing Question 4 Single-choice Differentiating 2016_北京 Paper 4.(5 分)下列函数中,在区间(-1,1)上为减函数的是( ) A. $y=\frac{1}{1-x}$B. $y=\cos x$C. $y=\ln (x+1)$D. $y=2^{-x}$ Answer keyD ☆ SaveCan't do it, show the explanation查看原卷 →