A compound microscope is designed with two symmetric biconvex lenses. The objective lens is cut vertically, creating two identical plano-convex lenses. One of them is used in place of original objective lens. To retain same magnification keeping the object distance unchanged, the tube length has to be

A

increased two times

B

increased $$\frac{3}{2}$$ times

C

decreased two times

D

decreased $$\frac{3}{2}$$ times