Olivia and Helen can achieve gains from trade if$\_\_\_\_\_\_\_.$

A$.$

Helen sells pants to Olivia in exchange for some of the skirts that Olivia produces

B$.$

Helen sells both pants and skirts to Olivia in exchange for money

C$.$

Olivia sells pants to Helen in exchange for some of the skirts that Helen produces

D$.$

Olivia sells both pants and skirts to Helen in exchange for money