Differences between Feynman diagrams

I’m reading Weinberg’s paper on "Dynamics at Infinite Momentum" in which he proves a claim about the type of Feynman diagram that contributes finitely to the perturbation series and the type that contributes 0 in the infinite momentum frame. However, I don’t understand the differences between the following set of diagrams. How does the propagator in diagram B bending make the diagram different?