The control group is the part of an experiment that does not receive the variable and is used for comparison.
We would need to see the diagram in order to answer the question correctly. without the diagram we can't help
The southerly lowlands of the island average around 0 °C<span> (</span>32 °F) in winter, while the Highlands of Iceland tend to average around −10 °C<span> (14 °F). The lowest temperatures in the northern part of the island range from around −25 to −30 °C (−13 to −22 °F). The lowest temperature on record is −39.7 °C (−</span>39.5 °F<span>).</span>
