$\text{ The function }f\left(x\right)=\frac{\left[\log \right(1+ax)-\log (1-bx\left)\right]}{x}\text{ is not defined at }x=0\text{. The }$$\text{ value, which should be assigned to }f\text{ at }x=0\text{ so that it is continuous at }x=0\text{, is }$

• A

  $a+b$

• B

  $a-b$

• C

  $\log a+\log b$

• D

  None of these