sentence2_structure: the muscular and skeletal organs<>are known as<>the musculoskeletal system
sentence1: Organ systems to be studied include the skeletal, muscular, nervous, cardiovascular, endocrine, respiratory, digestive, excretory, and reproductive systems.
sentence2: Together, the muscular and skeletal organs are known as the musculoskeletal system.
question: Together, the muscular and skeletal organs are known as what?