急性肾小球肾炎循环充血状态多发生于（）
A.1个月内
B.1周
C.2周
D.3～5日
E.3周
参考答案：D
— I was awarded a prize for doing volunteer work.
— _____. [ ]
A. You've got it
B. You deserve it
C. Good idea
D. Here we are
如图所示，斜面长4m，高2m，工人用400N的力沿斜面将重为600N的箱子，从底端推到顶端．下列说法中正确的是
A．有用功为1800J，总功1200J
B．有用功为1200J，额外功为800J
C．总功为1600J，机械效率为75％
D．总功为800J，机械效率为75％
