The Formula for the Income Elasticity of Demand Can Be $\eta$

The formula for the income elasticity of demand can be written as:

A) $\eta$ _I = ( $\Delta$ Q / $\Delta$ I) (I / Q) .
B) $\eta$ _I = ( $\Delta$ I / $\Delta$ Q) (I / Q) .
C) $\eta$ _I = ( $\Delta$ Q / $\Delta$ I) (Q / I) .
D) $\eta$ _I = ( $\Delta$ I / $\Delta$ Q) (Q / I) .
E) none of the above.