Final answer:
Replacing 'repel' with 'interact' would most significantly alter the meaning of the passage on nuclear fusion, as 'interact' includes a variety of particle relationships, not just repulsion.
Step-by-step explanation:
The word "repel" plays a significant role in the context of nuclear fusion, where it refers to the electrostatic force that pushes positively charged nuclei apart. Replacing "repel" with "interact" would MOST CHANGE the meaning of the selection, as "interact" implies a broader range of possible relationships between particles, including attracting, which is the opposite of repelling. The words "resist", "oppose", or "separate" all suggest a similar concept to "repel", maintaining the idea of a repulsive force, and therefore these options would least change the meaning.