sentence questions

0 Hi, I was reading the book entitled "The Craft of Revision" by Donald Murray and I have questions on some sentences on page 14 of the book. Each course, corporation, or government agency has its own environment. You should never forget that in writing you are either apprentice or a practicing historian, psychologist, environmental planner, biologist, business manager. Each discipline has its own climate, its own expectations in written material. Rewrite of the above portion of the text: Each course, 1) corporation, or government agency has its own environment. You should never forget that in writing you are either apprentice or a practicing historian, 2) psychologist, environmental planner, biologist, business manager. Each discipline has its own climate, its own expectations in written material. 1) Why not 'a corporation' and 'a government'? 2) Can we lay out names of jobs/professions like that? Should there be the word 'and' before the last word in the list? 0-