All of the following are examples of commodity-linked equities EXCEPT:（）

A. a gold mining company

B. a supermarket operating company

C. an oil and gas exploration company

现有t1℃时某溶液l00g，溶质质量分数为20%，溶液密度为1.5g/mL，降温至t2℃时有5g晶体（不含结晶水）析出，则t2℃时溶液的溶质质量分数为（　　）

A．25.4%

B．20.3%

C．15.8%

D．5.9%