Hans is performing an experiment examining how salt affects the speed at which water freezes. He fills four equally sized containers with the same amounts of water. Then, in three of the containers, he stirs in varying amounts of salt. The fourth container remains plain water.

Hans places all four of the containers in the same freezer and checks the containers every five minutes, recording when the water in each container freezes solid.

In this situation, what do Hans’s time measurements represent?

A.
the response variable
B.
the control group
C.
the response group
D.
the explanatory variable