Which of the following statement can best distinguish between fat and thin people

A．Fat people are sullen and gloomy whereas thin people are cheerful who know no fatigue.

B．Fat people are lazy and clumsy whereas thin people are diligent and crafty.

C．Fat people are practically reliable whereas thin people are seldom trustworthy.

D．Fat people are always feeling jaded whereas thin people never feel tired.

如果二元物系，A₁₂<0，A₂₁>0，则此二元物系所形成的溶液一定是（）

A.正偏差溶液

B.理想溶液

C.负偏差溶液

D.不确定