Why do amines act as nucleophiles ?

Question

$\begin{array}{1 1} \text{(a)Due to the presence of protons on nitrogen of amines} \\\text{(b) Due to the presence of lone pair of electrons on nitrogen of amines} \\ \text{(c) Due to the presence of hydrogen bond on nitrogen of amines.} \\ \text{(d) Due to the presence of Oxygen bond on nitrogen of amines.} \end{array}$