Final answer:
Option (e), A disorder affecting the heart's electrical rhythm, muscle contraction, and bone composition is likely due to the endocrine system, which regulates these functions through hormone secretion.
Step-by-step explanation:
A disorder that causes changes in the electrical rhythm of the heart, the ability of skeletal muscle to contract properly, and bone composition would most likely be related to the endocrine system(e). The endocrine system is involved with hormone secretion which affects a wide range of bodily functions, including heart rate regulation through the release of adrenaline, muscle contraction through electrolyte balance, and bone composition through hormones such as parathyroid hormone and calcitonin.
While the nervous system also has an influence on the heart's electrical rhythm and muscle contraction, it is less likely to have a direct impact on bone composition compared to the endocrine system. Additionally, the nervous system's role is more about the rapid transmission of signals rather than sustained physiological changes that could affect bone composition.