What population could auditor have tested in his search for unrecorded liabilities for year ended December 31? Explain.

a. Checks written in the two weeks before year end (12/15 to 12/31)

b. Entries to the purchases journal between 12/15 and 12/31

c. Receiving reports dated 1/1 - 1/15

d. Receiving reports dated 12/15 to 12/31