While filling up the air bottle when necessary, one of the following ways is something very dangerous and that you should NEVER DO. Choose and mark this dangerous way that you shouldn't do.

A
Boosting the air, by means of auxiliary set
B
Boosting the air, by means of carbonic acid gas
C
Filling the air bottle with oxygen or hydrogen
D
Filling the air bottle with air compressor
E
Filling the air bottle with fresh air