永动机是不可能制成的，因为它违背了______定律．
永动机是不可能制成的，因为它违背了能量守恒定律．
故答案为：能量守恒．
The teacher told him to speak louder ________by everybody.
A．so as to be heard
B．so as to hear
C．in order that heard
D．in order to hear
对于普通公路，混凝土原材料按质量（重量）计，（）的误差不超过（）
