On August 31, 2011, Harvey Co. decided to change from the FIFO periodic inventory system to the weightedaverage periodic inventory system. Harvey is on a calendar year basis. The cumulative effect of the change is determined

a. As of January 1, 2011.

b. As of August 31, 2011.

c. During the eight months ending August 31, 2011, by a weighted-average of the purchases.

d. As of the earliest period presented if practicable.