One-half length of 50mm diameter steel rod is solid while the remaining half is hollow having a bore of 5mm. The rod is subjected to equal and opposite torque at its ends. If the maximum shear stress in solid portion is $$\tau$$ the maximum shear stress in the hollow portion is:

A

$$\frac{15}{16}\tau$$

B

$$\tau$$

C

$$\frac{4}{3}\tau$$

D

$$\frac{16}{15}\tau$$