According to the passage, what cause(s) the problem of childhood obesity in Britain()

A. Junk food.

B. Too little exercise.

C. An increasingly sedentary life style.

D. All the above.

在动态分区算法中，（）倾向与优先利用内存中的低地址部分的空闲分区，从而保留了高地址部分的大空闲分区。