it has proved or it has been proved

选2 被动语态，表示“被证明、被证实”

不过，用过去分词proven的表达会更多一些：has been proven，表示“被证明、被证实”的状态:

Preventative medicine has been proven to be the most effective way of reducing the incidence of fatal childhood diseases.

2是对的。
因为主语是entative medicine，所以要用被动，所以是has been proved

2)
Preventative medicine has been proved to be the most effective way of reducing the incidence of fatal childhood diseases是对的，
被证明要用被动时态

2)
Preventative medicine has been proved to be the most effective way of reducing the incidence of fatal childhood diseases.