由9、6、5、0、2、1组成的最大六位数是______，最小六位数是______．

While you are working in a space，the fixed CO₂ system is accidentally activated．You should（）.

A.Secure the applicators to preserve the charge in the cylinders

B.Continue with your work as there is nothing you can do to stop the flow of CO₂

C.Retreat to fresh air and ventilate the compartment before returning

D.Make sure all doors and vents are secured