凸轮的损伤形式有凸轮工作表面（）、（）和（）。
参考答案：磨损、擦伤、疲劳剥落
—Where is your mother, Alice?
—She's gone to the office; she has left a ______ saying that she has something important to do. [ ]
A. excuse
B. information
C. news
D. message
— Is this your MP3, Kathy?
— No. ______ is in the bag.
A．My
B．Mine
C．Your
D．Yours
