I think that the best phrase to fit into the blank is a "scientific theory".
A scientific theory is developed through experiments which use the scientific method, and a theory can be improved if additional data is available or if people provide suggestions which make the theory fit the data better.
Answer:
An increase of 3,500 J
Explanation:
Given that,
Energy added by swimmer = 12000 J
Heat removed by the surrounding = 8500 J
We need to find the total change in energy. It can be calculated using the law of conservation of energy such as :

As the change in energy is positive, it means that there is an increase of 3500 J.
Answer:
I believe that it is the lettuce.
Explanation:
it is the fist thing in the graph so it is the start/producer of the chain.