人体形成视觉的部位在（　　）

A．视网膜

B．晶状体

C．玻璃体

D．大脑的视觉中枢

Which is the proper method of determining whether a portable CO₂ fire extinguisher needs recharging?（）

A.Check the tag to see when the extinguisher was last charged

B.Release a small amount of CO₂; if the CO₂ discharges，the extinguisher is acceptable

C.Weigh the extinguisher and compare the weight against that stamped on the valve

D.Recharge the extinguisher at least once each year