预防肠道传染病的综合措施中，应以哪一环节为主（）

A.隔离治疗病人

B.隔离治疗带菌者

C.切断传播途径

D.疫苗预防接种

E.接触者预防服药

Which of the following best explains the slope of the yield curve（）

A. The term spread between the yields of two maturities.

B. The credit spread between two securities with different maturities.

C. The nominal spread between two securities with different maturities.