You just chose the right answer. Triphenylphosphine has a lone pair of electrons.
(Phosforos has 5 valence electrons, s²p³, but there are 3 valence electrons used by the 3 Phenyl-groups, so there are just 2 valence electrons left for the bonding with Fe.)
 

Fe0             = 8e- (5-C5H5) = 5e- COT         = 2e- CH3          = 1e- PPh3         = 2e-                      18e-

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