设备在市场上维持其价值的时期称为()。
A.经济寿命
B.自然寿命
C.物质寿命
D.有效寿命
参考答案:D
— __________________
— There is a bed and a closet.[ ]
A. What's it?
B. Where's it?
C. What's in the bedroom?
决定电位离子层