（）《特种设备质量监督与安全监察规定》中规定，门锁、安全钳、限速器、缓冲器等重要安全部件，必须具有有效的型式试验合格证书。
参考答案：对
_______with his graduation design, he has been working in the library for a week.
A．Having occupied
B．Occupying
C． Being occupied
D．Occupied
一批彩电，经过两次降价后价格由原来的每台2250元降为1440元，问平均每次降价的百分率是多少？
