A=ø is subset of any set
A真包含于C => C is a non-empty set
B={x|(x+1).(x²+3x-4）=0 x∈R}
= {x|(x+1)(x+4)(x-1)=0 x∈R}
= {-4,-1,1}
C包含于B => C is a subet of {-4,-1,1}
A真包含于C包含于B => C is a non-empty subset of {-4,-1,1}
{-4},{-1},{1}, {-4,-1},{-4,1},{-1,1}, {-4,-1,1}