$$B_1$$ is a point on the side $$AC$$ of $$\triangle ABC$$ and $$B_1B$$ is joined. line is drawn through A parallel to $$B_1B$$ meeting $$BC$$ at $$A_1$$ and another line is drawn through $$C$$ parallel to $$B_1B$$ meeting $$AB$$ produced at $$C_1$$. Then

A

$$\frac{1}{CC_1} - \frac{1}{AA_1} = \frac{1}{BB_1}$$

B

$$\frac{1}{CC_1} + \frac{1}{AA_1} = \frac{1}{BB_1}$$

C

$$\frac{1}{BB_1} - \frac{1}{AA_1} = \frac{1}{CC_1}$$

D

$$\frac{1}{AA_1} - \frac{1}{CC_1} = \frac{2}{BB_1}$$