写出称量误差来源中，你认为主要的三种：（），（），（）。
参考答案：称量过慢，物体吸炒；砝码磨损沾污，未校准；被测物体的温度太高或太低，与天平室温不平衡
David apologized to me yesterday. __, I won't forgive him for it was not the first time that he had hurt me.
A．If so
B．If ever
C．Even so
D．Even though
计算题：已知，一孔炭化室装煤20.6吨，煤水分为7%，求实际干煤为多少？
