Final answer:
The central image in Frost's 'Design' is a moth trapped by a spider, which serves to explore themes of natural design and randomness.
Step-by-step explanation:
The central image in Robert Frost's poem Design is A. a moth trapped by a spider. This image serves as the foundation for the poem's exploration of themes such as the existence of design in nature, the randomness of events, and the intersection of death and beauty. Frost's use of a traditional sonnet form with an unconventional twist mirrors the poem’s thematic questioning of order and chaos. The white spider on a white heal-all flower holding the white moth raises questions about the randomness or intentionality behind such occurrences in nature.