After reading the paragraph below, answer the questions that follow.
In 2011, scientists investigated whether the salts that are spread on icy roads to melt the ice are diluted enough by spring rainfall so that they do not have negative effects on amphibian species that breed in nearby areas. They exposed clutches (groups of eggs) of salamanders to three test conditions with varying salt concentrations (road salts mixed with dechlorinated tap water) to simulate salt concentrations of small pools of water located near highways that are typically fed by rain—areas where salamanders often lay their eggs. After 9 days, the scientists placed the three groups in "normal" water and measured how much body mass the salamanders lost every 3 days for 9 days. They chose to measure change in mass because salamanders are able to take in water, which helps lower the chances of salamander embryos dying from freezing, disease, or predation. The table below provides partial results of this study.
| Group | Chloride Concentration in Test Conditions | Total % Mass Lost after 9 Days of Exposure to Test Conditions | Total % Mass Regained after 9 Days in Normal Water Conditions | Additional % Mass Lost after 9 Days in Normal Water Conditions |
| 1 | 145 mg/L | 20% | 15% | 0% |
| 2 | 945 mg/L | 35% | 0% | 10% |
There was a third group (group 3) in this study that experienced the same test conditions as groups 1 and 2
except that the water to which group 3 was exposed always had a chloride concentration (mg/L) that salamander clutches would normally experience (that is, with no road salts in the water). How would you describe this group?
◦ a dependent variable
◦ an experimental group
◦ an independent variable
◦ a control group
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