Circumferential and longitudinal strains in the cylindrical boiler under internal steam pressure are $$ε_1$$ and $$ε_2$$ respectively. Change in the volume of the boiler cylinder per unit volume will be

A

$$ε_1 + 2 ε_2$$

B

$$ε_1 ε_2^2$$

C

$$2ε_1 + ε_2$$

D

$$ε_1^2 ε_2$$