There is no official rule about the use of the word "being." The GMAT just tends to use it in awkward and/or passive constructions; therefore its presence is generally a sign of a wrong answer. If it's in a correct choice, it is most likely to appear at the beginning of a sentence, as in this example:
"Being the president is both difficult and rewarding."
Naturally, if "being" is in the non-underlined portion, or if it appears in every answer choice, then it is
being used correctly. Still, most of its uses are not so good. Here are some examples of GMAT-style wrong choices containing "being":
I was not aware of of the situation being so bad. (Better is: I was not aware that the situation was so bad.)
He was not interested in working hard, but being rich. (Better: He was interested not in working hard, but in becoming rich.)
The CFO suggested a reduction in the number of employees being assigned to the project. (Better: Simply remove "being.")
These are just a few examples. It may help to spend some time looking through SC questions that contain "being" and asking "What purpose does the word serve here? Could it be replaced with something better, or simply eliminated? Is there a more direct way to say this that would not require the use of 'being'?"
Still, if you need to make a quick decision, avoiding "being" is usually the way to go.
I hope this helps!
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