A:东北平原湿地面积减少,生态环境恶化
B:华北平原遭受旱涝、盐碱、风沙威胁
C:黄土高原植被覆盖率低,水土流失严重
D:华北平原灌溉水源充足
Air pollution has become ______ than ever before. We must do something to stop it.
下列做法中,属于增大摩擦的是( )
(Ⅰ)求f(x)的单调递增区间
(Ⅱ)若sin2x+af(x+ π6 )+1>6cos4x对任意x∈(﹣ π4 , π4 )恒成立,求实数a的取值范围.