2. why is an experiment called a controlled study?

An experiment is termed a controlled study as a result of the person conducting the experiment are going to be able to control the controllable variables or factors. The person conducting the experiment will manipulate the variables apart from the independent variables and therefore the variety of times the experiment are going to be done.

Explanation:
In a controlled exposure study, one cluster of participants is exposed to a substance (e.g. a pollutant) whereas those within the"control" group aren't. The results are then compared to work out the health effects of the substance being studied.

A controlled experiment could be a scientific test done underneath controlled conditions, which means that only one (or a few) factors are modified at a time, whereas all others are kept constant.

The correct answer is  "c".  it is "c" because melting is an endothermic change, and endothermic get's energy from surroundings.