Answer:
The fourth plant that receives pure water is the control group.
Explanation:
The election of a control group is essential in an experiment. Its principal purpose is to allow the discrimination of the results obtained by the treatment in the study, in this case, <em>the different concentrations of salty water that each plant receives</em>. The control group provides a reference point. It must be selected from the same population of the treatment groups. Both groups must be similar in every variable that might influence the results, <u>except for the study treatment.</u>
<span>A stem is one of two main structural axes of a vascular plant, the other being the root. The stem is normally divided into nodes and internodes. The nodes hold buds which grow into one or more leaves, conifer cones, roots, other stems, or flowers (inflorescences); the internodes distance one node from another.</span>
The golf would weigh less than a gram, and the ball, if hit hard, would fly at least very far away due to the kinetic energy without any atmospheric drag.
You forgot to put the options, but i believe it is magma.