Some people view the findings with caution, noting that a cause-and-effect relationship between passive smoking and cancer remains ().

A. to be shown

B. to have shown

C. to have been shown

D. being shown

预防HBeAg阳性母亲所生的新生儿感染HBV最有效的措施是（）

A.丙种球蛋白

B.乙肝疫苗

C.高效价乙肝免疫球蛋白

D.乙肝疫苗加丙种球蛋白

E.高效价乙肝免疫球蛋白加乙肝疫苗