The circles whose equations are x² + y² +c² = 2ax and x² + y² + c² −2by = 0 will touch each other externally if?

A. 1/b² +1/c² = 1/a²
B. 1/c² +1/a² =1/b²
C. 1/a² + 1/b² =1/c²
D. None of these