The ratio of lengths, radii and Young's moduli of steel to brass wires in the figure are $$\alpha$$, $$\beta$$ and $$\gamma$$, respectively. The corresponding ratio of the increase in their lengths is

A

$$\frac{2\alpha}{3\beta^2\gamma}$$

B

$$\frac{5\alpha}{3\beta^2\gamma}$$

C

$$\frac{2\alpha\beta^2}{3\gamma}$$

D

$$\frac{5\alpha\beta^2}{3\gamma}$$