The extent of the testing of detail tie-in of an aged trial balance depends on all but which of the following?

The extent of the testing of detail tie-in of an aged trial balance depends on all but which of the following?

a. The number of accounts involved.
b. The degree to which the master file has been tested as a part of tests of controls tests of                             transactions.
c. The extent to which the schedule has been verified by an independent person before it is given                   to the auditor.
d. The extent of testing depends on each of the above.