Laurie and Abby decide to make guacamole dip with chips to bring to a party. Laurie used a type of avocado called a Hass Avocado and Abby used a type of avocado called a Fuerte Avocado. Laurie and Abby both made their guacamole dip the same way except for one thing...Abby put lemon juice in hers to give it a 'tang.' When the girls uncovered their dip at the celebration, Laurie's had turned a brownish green but Abby's was still bright green. The girls wondered if adding the lemon juice to Abby's guacamole dip had helped it stay a nice bright green.

Hypothesis:

What is another variable that Laurie and Abby could test in this situation in a 2nd experiment?