Controls are defined as _​

The second one is the answer

I think things that are kept constant during an experiment is right.

Explanation:

in the analysis of systems that involve fluid flow, we frequently encounter the combination of properties u and pv.

each chemical family is represented as a group or column on the periodic table. based on chemical properties, there are 6 types of chemical families. group 1 represents alkali metals, group 2 represents alkaline earth metals, groups 3 to 12 represent transition metals, groups 13 to 16 represent non-metals and other metals, group 17 represents halogens and group 18 represents noble gases.