Students hypothesized that water pollution affects the growth of fish. in an experiment, they added the same amount of food to ponds polluted by fertilizers and industrial waste. they measured fish growth and found that most fish grow more slowly in each of these environments. what part of their experiment did they forget to include?

The correct answer will be control group.

Explanation:

A scientific experiment is designed in such a way that it should include two types of groups: the experimental group in which the variable has to be tested and the control group in which the variable to be tested is kept constant.

Since in the given question, the experiment was performed to test that water pollution affects the growth of fish, so the independent variable will be the "pollution".

The experiment was performed in which pond was polluted with fertilizers which will provide the experimental data but he forgot to prepare a control group which will provide the reference to the experimental data.

Thus, the control group is the correct answer.

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.