In order to keep the balance of ecosystem, every possible means _______to deal with the problems of the over-exploiting of natural resources.

A．has tried

B．has been tried

C．have taken

D．have been taken

预防病毒肝炎的免疫方法（）

A.丙种球蛋白对甲肝有一定作用

B.丙种球蛋白对甲肝没有作用

C.丙种球蛋白对乙肝没有明显作用

D.乙型肝炎可以采用高纯度HBsAg疫苗

E.母婴对甲肝、乙肝有保护作用