判断定于从句,可以做简法.
A不行,简化后相当于是who will tell you about it.这句话应该是陈述语气.
这题C应该可以,简化后相当于Those will tell you about it.
Those who knows the truth那些知情的人.
有句谚语叫做God helps those who helps themselves.
之所以不选C,应该是和上下文的意思有关.