氟里昂过滤器采用网孔为（）mm的铜丝网制成。
A.0.1～0.2
B.0.2～0.3
C.0.3～0.4
D.0.4～0.5
参考答案：A
A closed-end fund:（）
A. is traded in the primary market but not the secondary market.
B. has its price determined by supply and demand, regardless of its net asset value (NAV).
C. has its price determined by the net asset value (NAV).
洁净工作台的安放位置应尽量远离振源和声源，以避免环境振动和噪声对它的影响。( )
