When comparing the adjusting process under the perpetual and periodic inventory systems,

a$.$ the cost of goodsisold account is reduced by the cost of estimated returns inventory for the current year under the perpetual inventory system.

b$.$ the ending inventory is determined by a physical count under both systems.

c$.$ no entry is made for estimated returns inventory under the periodic inventory system.

d$.$ the inventory shrinkage adjustment is the same under both systems.