Answer:
C). The speaker alludes to rivers as old as civilization itself.
Step-by-step explanation:
Allusions are demonstrated as the inclusion of a short reference in a literary work(poem or prose) which could either be direct or indirect referring to a historically, politically, or culturally significant place or person or idea. These are involved in a literary work with an aim to nurture the context and meaning of the work due to making it more vast and complex.
As per the question, the allusion in the given excerpt from "The Negro Speaks of Rivers" by Langston Hughes exemplifies the reference of 'civilization' to expand the context and description of the 'river' in order to enhance its meaning and impact further. Therefore, option C would be the correct answer.