For Mrs. Nygaard’s two-way table summarizing the preferences of her class regarding the field trip options (the zoo or the aquarium), the most appropriate row and column headings would be:
Row headings: Gender (boys and girls)
Column headings: Field trip preference (zoo and aquarium)
Thus, the correct description from your options is:
gender and field trip preference
This option reflects the two categories being analyzed, which are the students' gender and their preferences for the type of field trip.