The two dry sand samples are examined by changing one parameter. The independent variable, the one that is intentionally manipulated between the two samples, is the

the first box is correct

The two dry sand samples are examined by changing one parameter. The independent variable, the one that is intentionally manipulated between the two samples, is the  Mass of each sample

the second box as well

Besides the amount of material, there is also another variable that is manipulated within each of the two mass groups and represented as three types. This independent variable is the type of material used

& the third box

In each case, the dependent variable, the one that you measure the response in, is the temperature over time

mass of each sample.

Explanation:

The quantities that are able to change in an experiment or a research are called as the variables. It is a trait or any factor that exits in different types or amounts. An independent variable is changed by the scientist or the experimenter in the experiment. Its value does not depends on the experiment.

In the context, there are boxes of two dry samples of sand and they are examined by changing one of the parameter. It is the independent variable that is manipulated in the two samples is the mass of each of the sample.