The six steps of the scientific are:
1. State the question
2. Conduct research
3. Create a hypothesis
4. Perform the experiment
5. Analyze the data
6. Conclusion
So D. would be the correct answer, even though communicating the results could possibly be a step if it's required.
The dependent variable is the slime on Gary's shell, because it's depending on other factors (independent factors).
It would last as long as the applied force continued, or until the accelerating object hit something.
