The Boussinesq’s vertical pressure σz under a uniformly loaded circular area is given by ________

• A. \(σ_z=q\left[1-\left[\frac{1}{1+(\frac{a}{z})^2}\right]^{\frac{3}{2}}\right] \)
• B. \(σ_z=q\left[1+\left[\frac{1}{1+(\frac{a}{z})^2}\right]^{\frac{3}{2}}\right] \)
• C. \(σ_z=q\left[\frac{1}{1+(\frac{a}{z})^2}\right]^{\frac{3}{2}} \)
• D. \(σ_z=q\left[1-\left[\frac{1}{1+(\frac{a}{z})^2}\right]^{\frac{5}{2}}\right] \)