The recent teacher shortage in Monmouth Public Schools is

i would choose C here since it mentiones teacher again.

The recent teacher shortage in Monmouth Public Schools is because there has not been a new contract nor have they seen any improvements in working conditions.

(A) is because there has not been a new contract nor have they seen any improvements in working conditions.
---->flawful, "they" is ambiguous and unparallel structure ---> out

(B) has been due to the lack of a new contract and because they have seen any improvements in working conditions.
-----> NOTE : According to GMAXonline, the answer choices with " because" are ALWAYS preferred to those with "due to" ---> out

(C) is because there has neither been a new contract nor have teachers seen any improvements in working conditions.
-----> unparallel structure ----> out

(D) is because there has neither been a new contract nor have there been any improvements in working conditions.
------> perfect!

(E) are because there has not been a new contract nor have teachers seen any improvements in working conditions.
"are" is wrong and also there's no parallelism ----> out

D it is.

Looks like C .. D is changing the meaning, teacher sees the improvement in working conditions..but in D something else is mentioned.

Bingo! OA is C.

OE:

Rule and Fix:
A Pronoun must clearly and correctly refer to only one thing. "They" is plural and the only plural noun before it is "schools" which cannot be what it should refer to.

POE:
A and B because of the pronoun.

Chunk and Compare:
Compare C and D to E.
C and D both use the singular verb "is" where E uses "are". Since the subject that the verb refers to is "shortage" the verb should be singular.

Eliminate E.

Compare C to D. The difference is C specifically mentions the teachers while D does not. Since the GMAT values clarity so C is better than D.

:thanks I will keep this in mind.