Stucture B is formed by tract:
Nerve fibers entering and leaving the cerebellum pass through superior middle and inferior cerebellar peduncles which connect the cerebellum to midbrain, pons and medulla respectively. Middle cerebellar peduncle is made up of pontocerebellar fibers.
Pontocerebellar
Olivocerebellar
Vestibulo cerebellar
Anterior spinocerebellar