Answer:
The height to which to tomato plants grow
Step-by-step explanation:
In an experiment, the dependent variable is the variable that the experimenter measures. It is the variable that responds to changes made to the independent/manipulable variable.
According to this question, students investigate how soil pH affects the height of tomato plants. The different pH each plant receives is the independent variable while the HEIGHT OF THE PLANTS that responds to the soil pH or that is measured by the students is the DEPENDENT VARIABLE.