Answer:
independent variable: the herbicides, the number of hours
dependent variable: the number of plant which died
control variables: the amount of seeds, herbicide amount, the water amount, the sun light
Step-by-step explanation:
the independent variables: those modified by the researcher during the experiments. In this case, the kind of herbicide and the time are variables changes in the study by the researcher.
the dependent variables: those which are not controlled directly by the researcher but are impacted by the changes of the independent variables. In this case, the amount of plant that died.
The control variables: are constant elements in the research, in this case the amount of waters, the amount of sprayed herbicide are constant, so the study never try to understand how a change of this variables affect impact the experiment.