细胞膜功能的复杂程度,主要取决于膜上的 ( )
A:磷脂含量
B:蛋白质的种类和数量
C:糖的种类
D:水含量
____
如图,AO⊥平面α,点O为垂足,BC⊂平面α,BC⊥OB,若∠ABO=π4,∠COB=π6,则cos∠BAC=____
Progress suggests a person's ability to change the way he is living at the moment and it must ______ a better life and a better way of doing things.