Among the following amines, the strongest Bronsted base is 

Hint: sp3 nitrogen atom is more basic than sp2 nitrogen atom
Aniline is a weaker base than NH3 due to the delocalization of the lone pair of electrons of the N-atom over the benzene ring. Pyrrole is also basic than aniline and ammonia because the lone pair of electrons on the N-atom is donated towards aromatic sextet formation.
Therefore, pyrrolidine is the strongest base as lone pair oi nitrogen does not involve in resonance, and also due to the presence of two alkyl ring residue, basic strength becomes high among given four compounds.