The dependent in this case would be the type/quality of chairs as that is what you are changing.
Answer:
The answer is D. All of the above.
Explanation:
All of these were efforts and been effective.
If Adam is pulling with a pulling force of 120N, and the nets pulling force is 200N, and they are both going north, then that means that Krystal would have a a pulling force of 80N north, as 200N- 120N is 80N. She would be pulling north because she is on the same side as Adam, helping to pull the sled upwards.
-Hope this helps! xo