Are humans a compound or a mixture?

Which direction does the energy flow in this energy pyramid ?

Which of the following is not a type of epithelial cell

Ascientist is designing an investigation to study the impact of invasive bird populations on local, native bird populations at backyard bird feeders. what population is most likely to be a control group for the investigation? amount of food number of bird feeders invasive bird populations local backyard birdfeeders without food