Which of the Following Is the Z-Score Equation for the Ith

Which of the following is the z-score equation for the ith observation?

A) Zt ₌ $\sqrt { \frac { x _ { i } - \bar { x } } { s ^ { 2 } } }$
B) Zᵢ ₌ $\frac { x _ { i - \bar { x } } } { S }$
C) Z₁= (xᵢ ₋ $\bar{x}$ ) S
D) Zᵢ = $\frac{x_{i}}{s\left(x_{i}-\bar{x}\right) }$