The Number of Degrees of Freedom for a Two-Way Contingency $I \cdot J$

Multiple Choice

The number of degrees of freedom for a two-way contingency table with I rows and J columns is

A) $I \cdot J$
B) $( I - 1 ) \cdot J$
C) $I \cdot ( J - 1 )$
D) $( I - 1 ) \cdot ( J - 1 )$
E) $I + J - 1$