What is the value of volumetric strain in a thin walled cylindrical vessel with modulus of elascticity E, Poisson’s rate 
and of diameter ‘d’, will thickness ‘t’ and subjected to internal fluid pressure P?
(a) $\frac{pd}{4tE}.(5-4\mu )$
(b) $\frac{pd}{3tE}.(4-3\mu )$
(c) $\frac{pd}{2tE}.(3-2\mu )$
(d) $\frac{pd}{tE}.(2-\mu )$