The passage below describes an experiment. Read the passage and then follow the instructions below.

Gabby planted 25 tomato seeds one-half inch below the soil surface in each of six pots. Gabby added an equal amount of fertilizer to three of the six pots. She placed the pots in a plant growth chamber where all the seeds experienced the same temperature, amount of light, and humidity level. After two weeks, Gabby counted the number of seedlings that grew in each pot. She compared the number of seedlings in the pots with fertilizer to the number of seedlings in the pots without fertilizer.


Identify the question that Gabby's experiment can best answer