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