Although an Amine Nitrogen Atom Containing an Electron Pair

Although an amine nitrogen atom containing an electron pair and bonded to three different groups is technically a stereogenic center, the chirality of the amine nitrogen is often ignored.Why is that?

A) Because four bonds are needed to define a stereogenic center.
B) Because chirality only exists with the tetrahedral carbon atoms.
C) Because there is usually slow interconversion between the two isomeric forms at room temperature.
D) Because there is usually rapid interconversion between the two isomeric forms at room temperature.