Au Nigéria, la plupart des pècheurs (vivre) au bord des fleuves.

In the given sentence, "Au Nigéria, la plupart des pécheurs (vivre) au bord des fleuves," we need to choose the correct form of the verb "vivre" (to live) to complete the sentence. The subject here is "la plupart des pêcheurs," which translates to "most of the fishermen." This subject indicates that we are dealing with a plural form, since "most of the fishermen" refers to more than one person. Therefore, we must choose the verb form that matches a plural subject.

In French, the verb "vivre" is conjugated as follows:

• je vis (I live)
• tu vis (you live)
• il/elle/on vit (he/she/one lives)
• nous vivons (we live)
• vous vivez (you all live)
• ils/elles vivent (they live)

Given that "la plupart des pêcheurs" is plural, the correct conjugation for "vivre" in this context is "vivent."

Thus, the completed sentence is: "Au Nigéria, la plupart des pécheurs vivent au bord des fleuves."