The Most General Rule That Governs Degrees of Freedom Is $\Sigma$

Multiple Choice

The most general rule that governs degrees of freedom is that

A) df = N-1
B) df = $\Sigma$ (X - $\bar { X }$ ) ²
C) degrees of freedom depend on the $\alpha$ level
D) degrees of freedom depend on the number of observations minus the number of parameters estimated with statistics.