HELP PLEASE Which of the following is a good description of biological clocks?
a) A light-dark cycle of 24 hours during which entrainment takes place
b) External chemical systems that are regulated by time and control circadian rhythms c) None of these
d) Internal chemical systems that are regulated by nature and control parts of the body

What are the characteristics of living things

Are the earth's ocean floor and continents the same age geologically? why or why not?

Which of the following matches the organisms described with the correct domain? a. archaea--multicellular, eukaryotic organisms that do not have cell walls b. eukarya--single-celled and multicellular organisms, with a defined nucleus and a variety of nutritional sources c. bacteria--unicellular, eukaryotic organisms with cell walls that do not contain peptidoglycan d. bacteria--unicellular, eukaryotic organisms that always lack cell walls