已知某二元体系在某温度下汽相可看做理想气体，在x₁=0.4时，y₁=1.197，y₂=1.083，在此温度下蒸气压为p^s₁=20kPa，p^s₂=25kPa，与x₁=0.4平衡的汽相组成y₁为（）。

A、0.629 

B、0.444 

C、0.555 

D、0.371

The contract is signed by the buyer and the seller in two original copies，______party holds one copy.

A．both B．each C．two D．either