a) The cost, and size of computers are decreasing, almost as rapidly as processing power is increasing.
b) Database management systems were originally large, unwieldy, and difficult to use.
c) A factory closing means the community loses jobs tax revenues and retail sales.
d) An operating system is the set of instructions, that directs the overall operations of the computer.
Would b) be the correct answer?
You seem to have a good grasp of comma usage. Example B demonstrates the use of the ...