Answer:
Celia should use the transition "becoming a" to clarify the relationship between ideas in the sentence.
The full sentence with the transition would be: When grizzly bears find food that has been improperly disposed of, they associate "easy food" with humans, becoming a nuisance animal over time.
The transition "becoming a" helps to show that the previous clause about grizzly bears associating humans with easy food is leading to the consequence of the bears becoming a nuisance animal over time.
Step-by-step explanation: