Final answer:
The dependent variable in Dr. Liu's study on the effects of violent television on six-year-old children is the children's behavior on the playground, making option 3 the correct answer.
Step-by-step explanation:
In Dr. Liu's study on the effects of violent television on six-year-old children, the dependent variable is the children's behavior on the playground.
This is because the dependent variable is expected to change based on the type of television content they watched, which serves as the independent variable.
Hence, the correct answer is option 3, the behavior on the playground, as it is the aspect of the study that is being measured to determine the impact of viewing either violent or nonviolent TV shows.