For a cohesive backfill with surcharge q, when at depth z₀, pₐ=0, then the depth z₀ is ___________

• A. \(z_0=\frac{q-2c cot⁡α}{γ} \)
• B. \(z_0=\frac{2c tan⁡α}{γ}-\frac{q}{γ} \)
• C. \(z_0=\frac{2 cot⁡α}{γ}+\frac{q}{γ} \)
• D. \(z_0=\frac{cot⁡α}{γ}-\frac{q}{γ} \)