In the pair of equations $a_{1}x + b_{1}y + c_{1} = 0$ and $a_{2}x + b_{2}y + c_{2} = 0$,if ............ then it has a unique solution.

• A
  $a_{1}b_{2} \neq a_{2}b_{1}$
• B
  $a_{1}b_{2} = b_{1}a_{2}$
• C
  $b_{1}c_{2} = c_{1}b_{2}$
• D
  $c_{1}a_{2} = a_{1}c_{2}$