— Who was on duty last Friday?
— . [ ]
A. I am
B. I was
C. Yes, I was
D. No, I wasn't
答案:B
火柴可以擦燃也可点燃,前者属于______的方法改变内能;后者属于______的方法改变内能.
简述乳铁蛋白的活性作用。