在呼吸运动中，肺主（）气，肾主（）气。
参考答案：摄；纳
_____ different life today is ____ what it was 20 years ago. [ ]
A. How; from
B. What a; from
C. What; from
D. How; than
氟化水源防龋的标准浓度是
A．0.5～1ppm
B．0.05～0.1ppm
C．5～10ppm
D．0.1～0.5ppm
E．1～5ppm
