An equi-convex lens of focal length $$f$$ is cut along a diameter, in two halves. The two identical pieces of the lens are now arranged as shown in the figure on a common axis at a separation $$f$$ between the two. The image of an object AB placed at $$x=0$$ cannot be formed at the distance $$x=\xi$$ from the object along the axis, for the value of $$\xi$$ as

A

$$\xi=2f$$

B

$$\xi=3f$$

C

$$\xi=4f$$

D

$$\xi=\infty$$