The inside and outside radii of a thick-walled cylindrical pressure vessel are denoted by a and b, respectively. If the vessel is subjected to an internal pressure P, then the magnitude of radial stress is \(\sigma_{rr}\) is

• A. zero at r = a and maximum at r = b
• B. maximum at r = a and zero at r = b
• C. constant over the entire thickness
• D. zero at both r = a and r = b