The correct answer is C. while and however
Step-by-step explanation:
The text explains the differences and similarities between seagulls and wild geese, which are two species of birds. Additionally, in the text, the author uses a compare/contrast structure because the author explains the common points of both species as well as their differences. Also, this is possible through specific clue words that show the similarities and differences.
In the case of differences, the author uses clue words such as however, while or on the other hand. This can be seen in "On the other hand, seagulls are scavengers, while wild geese aren't" that contrasts the diets of these species or in "However, they don't follow seasonal patterns of migration like wild geese" that shows the differences in migration. Thus, the words while and however are used to show contrast.