这句话主语 谓语 表语是那个

It 形式主语
to tell who is right 真正的主语
第一个is是谓语
is rather difficult 是表语

It is rather difficult to tell who is right
形式主语 谓语 表 语 真 正 主 语

主语 to tell who is right

谓语 is
表语 rather difficult

主：to tell who is right
谓：is
形式主语：it
表：rather difficult

主语 who is right
谓语is
表语difficult to tell

It主
is系
difficult表