Why is astronomy referred to as observational science and not primarily experimental science

What is a difference between systemic and pulmonary circulation? a. systemic circulation carries oxygenated blood to the lungs and pulmonary circulation carries deoxygenated blood to the body. b. systemic circulation carries deoxygenated blood to the lungs and pulmonary circulation carries oxygenated blood to the body. c. systemic circulation carries deoxygenated blood to the body and pulmonary circulation carries oxygenated blood to the lungs. d. systemic circulation carries oxygenated blood to the body and pulmonary circulation carries deoxygenated blood to the lungs.

Which of the following organisms are capable of self-fertilization? a.plants b.tigers c.humans

Prokaryotic and eukaryotic cells are different in many ways other than the presence or absence of a nucleus. if both archaebacteria and eubacteria are prokaryotic cells, then why are archaebacteria more closely related to eukaryotic cells than they are to eubacteria?