Which of the Following Record Validation Rules Prevents the User

Multiple Choice

Which of the following record validation rules prevents the user from entering the same value into both Field1 and Field2?

A) ([Field1] is Null) XOR ([Field2] is Null)
B) [Field1] < > [Field2]
C) (([Field1] > [Field2]) AND [Field2] >10) )
D) none of the above