人类呼吸的快慢是由（）决定的。
A.人体对氧气的需求
B.空气中的氧气含量
C.环境温度的高低
参考答案：A
He is packing his suitcase ______ his _______. [ ]
A. in, books
B. on, toys
C. with, clothes
D. for, fruit
