Being a realist, I could not accept her statement that supernatural beings had caused the disturbance.

(a) being a realist
(b) Since I am a realist,
(c) Being that I am a realist,
(d) Being as I am a realist,
(e) Realist that I am,

The answer is a. However I put down b. I have been constantly reminded never to use the word being....so why am i wrong here?

Hello,

This is true that being is almost incorrect choice in GMAT; however, this is one of the few ways for Being to be correct.

Here Being is used as a Gerund ( 'Verb plus ing' that takes the place of noun in a sentence ). Gerund phrase " Being a realist " is formed by linking verb be + ing. Since the gerund is based on a linking verb , the subject complement ( realist ) is necessary to acquire the complete meaning. Remember that linking verb cannot stand alone.

Being a realist is the subject of the sentence.

The word since ( as in answer choice b) is typically used to show some time reference. I am not sure if Since is correctly used here.

" I AM NOT A GRAMMAR EXPERT. MGMAT Instructors can probably shed more light on this issue.

To add to the above, 'since' is indeed used to show continuity of an action, however, 'since' can also mean 'because'.

In this sentence, you need a phrase to describe 'I' after the comma. 'Being a realist' is a gerund phrase that does the job.

I don't think choice B is ungrammatical, but choice A is marginally superior for at least two reasons:
(1) It's more concise.
(2) There's a little tension between the present tense of 'since I am' and 'I could not' in choice B, a tension that's circumvented by the use of a gerund phrase. Again, this combination of verbs isn't ungrammatical - choice B definitely isn't wrong enough to make the cut for the actual GMAT - but it's not as 'nice' as choice A.

What's Barron's explanation?