it should be "his being". That's how we use pronouns before a gerund. Also this question may be helpful as well http://www.gmatclub.com/phpbb/viewtopic.php?t=27429&highlight=helping
Correct, possessive pronouns are used before gerunds. But my problem is, how the heck do people recognize that being
acts as a gerund (noun) here?
I am guessing that the preposition tells you that it is a gerund, as examplified in this case as well:
Everyone of us has understood that without
his helping us we would not have succeeded in our program over the past six months.
This also means that "being" is 99% ruled out in GMAT but that 1% questions may be of this type.....
I doubt if being is a GERUND 'cos Gerund acts as a noun.
The rule I vaguely remember
[b]Objective forms of pronouns are usually used after verbs.
For eg: The teacher hated Sunil and me(used the objedtive form of "I")
But the exception to this rule is verb â€œbeâ€