These all are Lewis bases as N-atom in each of them has tendency to donate an electron pair. Piperidine (c) is the strongest base among these. In pyrrole (b) the lone pair of electron on $N$-atom is involved in delocalization of $\pi$ electrons (aromatic sextet) hence, it has least tendency to donate electron pair. Aniline $( d )$ and pyridine (a) are also weakly basic due to resonance.
On the other hand piperidine has no such delocalization and it is a secondary amine.
Hence, it is highly basic.