This one has a little trick. Once you see it, the question is actually pretty easy.

The key word here is "former." Assuming that Joan is still alive, she is the former chair of the planning board. But back then, she was just the plain old "chair," not the "former chair." The distinction is subtle, and in "real life" it would probably be OK to say she was the former chair, but not on the super-nitpicking GMAT. :mrgreen: Incidentally, I guess after 18 years, Joan just got sick and tired of being sat on all the time.

That eliminates A) - C). D) creates a "comma splice"--two independent clauses not joined by a coordinating conjunction.

And there you have it. Hope this helps, Mukherjee.