Bone-strengthening physical activity done increases bone-mineral content and bone density in youth. a. four or more hours a day b. every weekend c. three or more days a week d. twice a week every two weeks

Which property is used to identify the origin of an igneous rock? color density hardness crystal size

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

What is a photon? a. part of a ribosome b. a light particle c. a carbon dioxide molecule d. part of a chloroplast b. a light particle