The correct answer is "the scientific study of life or living things in all their forms." This is because biology is the branch of science that focuses on the study of living organisms, including their structure, function, growth, evolution, and distribution. It encompasses various sub-disciplines such as zoology, botany, microbiology, and genetics. Biology explores the complexity and diversity of life on Earth, from the smallest microorganisms to the largest ecosystems. It helps us understand the fundamental processes of life and how living organisms interact with their environment.