JEE Math Practice Question

If the expansion in powers of $$x$$ of the function $${1 \over {\left( {1 - ax} \right)\left( {1 - bx} \right)}}$$ is $${a_0} + {a_1}x + {a_2}{x^2} + {a_3}{x^3}.....$$ then $${a_n}$$ is

1. A.$${{{b^n} - {a^n}} \over {b - a}}$$
2. B.$${{{a^n} - {b^n}} \over {b - a}}$$
3. C.$${{{a^{n + 1}} - {b^{n + 1}}} \over {b - a}}$$
4. D.$${{{b^{n + 1}} - {a^{n + 1}}} \over {b - a}}$$