Answer:
The chemicals
Step-by-step explanation:
When a scientific experiment is proposed, it is necessary that the dependent and independent variables are identified.
An independent variable is one that does not need the influence of another variable and is responsible for presenting a result that depends on its manipulation. The dependent variable, on the other hand, is one that is influenced by the dependent variable and needs its manipulation to generate a result.
In the question above, we saw that Susan wants to know what results the manipulation of different chemicals will have on plant growth. With that, we can say that chemicals are the independent variable, while plant growth is the dependent variable.