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.