The VP of Finance wants to ensure that once an opportunity is closed, it cannot be modified by any user. How can an administrator meet this requirement?

A. Create a workflow field update to update the IsClosed field to True if a closed opportunity is modified
B. Set the Do Not Modify Closed Opportunity permission for all profiles
C. Set all fields to Read-Only on the standard Closed Opportunity page layout
D. Create an opportunity validation rule with the formula: PRIORVALUE(IsClosed) = True

Suggest answer: D

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