Riley can either change the surface area of the object or can change the slipperiness of the material.
When you add or change the subscript, you are changng the number of atoms in the substance.
D. this is because they consume less resources, but produce just as much power. if this is wrong, which i doubt, it is a.
Out of the three you gave ecosystem is what I would call the most broad. An ecosystem includes living AND non-living things in an area
Community is all the LIVING things in an area (plants are included and I think bacteria is too, but I'm not sure)
Population is pretty narrow it just looks at specific species in one area. Population of mosquitoes doesn't include butterflies, if only looks at mosquitoes
Hope this helped!