An investigation was carried out to model how sweating and evaporation of moisture from skin/fur affects the rate of heat loss in mammals.
One boiling tube (Setup A) was wrapped in a layer of dry paper towel, and another boiling tube (Setup B) was wrapped in an identical layer of wet paper towel. Both boiling tubes were filled with hot water and fitted with a rubber bung and thermometer.

Describe a control that could be used for this investigation.