If x^2 + 1/5x + a^2 is a perfect square, then a is?

Answer: Option C

$$\begin{array}{rl}& x^2+\frac{1}{5}x+a^2\\ & {\text{A}}^2+\text{2}\times \text{AB}+{\text{B}}^2={\left(\text{A}+\text{B}\right)}^2\\ & x^2+2\times \frac{1}{10}\times x+a^2={\left(x+\frac{1}{10}\right)}^2\\ & \text{A}=x\\ & \text{B}=\frac{1}{10}\\ & \text{B}=a=\frac{1}{10}\end{array}$$