My usual instruction to students when they are preparing to write their examinations is "think before you answer the questions". I am convinced that some multiple choice answers could be so close that you might not know the very one that answers the question correctly! Such is life. To choose your suitable dreams, you must think well!
When I was instructed to use medical oxygen to do my job at the W. M. Keck Observatory from 2001 to 2006, I was never told about the legal health information that is now posted on oxygen cylinders. My memories of the green medical oxygen cylinders that we would use daily is that they had no information on them and we were never given a recognised legal oxygen administration training course for routine daily use or a medical prescription from a doctor. We were shown the three oxygen cylinders at the facility and told to use them whenever we developed headaches, which was multiple times daily. It was common to find all three oxygen cylinders in use by other very high altitude workers and to have to line up to get a turn on the magical medical gas.