As the former chair of the planning board for 18 consecutive years and a board...

[Techsavvy]

As the former chair of the planning board for 18 consecutive years and a board member for 28 years, Joan Philkill attended more than 400 meetings and reviewed more than 700 rezoning applications.

A) As the former
B) The former
C) Former
D) She was
E) As the

Which completes the sentence most correctly and concisely?

[Ralf]

Hi,

I don't really understand your question when you say 'completes'. But

C) Former chair of...

sounds like a natural sentence header.
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[Yankee]

I'd say (E) As the is the best alternative:

As the chair of the planning board for 18 consecutive years and a board member for 28 years, Joan Philkill attended more than 400 meetings and reviewed more than 700 rezoning applications.

Reason:
I assume that Joan Philkill did the things mentioned during the entire time that she was a member of the planning board, and not (just) when or because she was the former chair of the planning board.
.
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[Ralf]

OOps, Amy's right, I obviously didn't read the subclause thoroughly...
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[Molly]

I'd say this is good alternative:

As chair of the planning board for 18 consecutive years and a board member for 28 years, Joan Philkill attended more than 400 meetings and reviewed more than 700 rezoning applications.