= Solution
{c}
There is one <one-particle-irreducible Feynman diagram>: an internal <photon> joins two points of the open <fermion> line, with the external <photon> attached to that line between them. It is the upper-left panel of the figure. Route internal <photon> <four-momentum> $k$ from the incoming side to the outgoing side; the adjacent internal <fermion> <four-momenta> are $p-k$ and $p'-k$. The <symmetry factor> is one.
The <vertex renormalization> <counterterm> is an additional local contribution when forming the renormalized <Feynman vertex>. External-leg <self-energy> insertions belong to the complete three-point <correlation function>, rather than this amputated <one-particle-irreducible Feynman diagram>.
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