The correct answer is $\boxed{\frac{1}{2}}$.
The circumferential stress is the stress that acts in a circle around the circumference of the cylinder. The longitudinal stress is the stress that acts along the length of the cylinder.
The ratio of circumferential stress to longitudinal stress is given by the following equation:
$$\frac{\sigma_c}{\sigma_l} = \frac{1 – \nu}{1 + \nu}$$
where $\nu$ is Poisson’s ratio. Poisson’s ratio is a dimensionless number that describes how much a material contracts in the transverse direction when it is stretched in the longitudinal direction.
For most materials, Poisson’s ratio is approximately equal to 0.3. Therefore, the ratio of circumferential stress to longitudinal stress is approximately equal to $\frac{1}{2}$.
Option A is incorrect because it is the ratio of the longitudinal stress to the circumferential stress. Option B is incorrect because it is the ratio of the circumferential stress to the longitudinal stress for a material with Poisson’s ratio equal to 0. Option C is incorrect because it is the ratio of the circumferential stress to the longitudinal stress for a material with Poisson’s ratio equal to 0.5. Option D is incorrect because it is the ratio of the circumferential stress to the longitudinal stress for a material with Poisson’s ratio equal to 1.