A Major Reason Explaining the Difficulty in Implementing Educational Reforms

A major reason explaining the difficulty in implementing educational reforms and achieving it desired effect is

A) they take so much financial support, and taxpayers are unwilling to raise budgets.
B) American education is a giant institution with standard operating procedures that set certain expectations.
C) teachers are set in their ways, and they refuse to change unless they can make all the decisions.
D) no one gives the changes enough time to take effect before they start assessing success or failure.