a + b + c = 0, then the value of a^2 + b^2 + c^2ab + bc + ca is?

Answer: Option B

$$\begin{array}{rl}& \text{If }a+b+c=0\\ & \text{Put }a=1,b=1\text{ and }c=-2\\ & \therefore \frac{a^2+b^2+c^2}{ab+bc+ca}\\ & =\frac{1+1+4}{1-2-2}\\ & =\frac{6}{-3}\\ & =-2\end{array}$$