The structure is D. a substrate
It binds lactose which changes its conformation so that is no longer binds to DNA. This allows the lactose operon to be transcribed.
Inquiry about nocturnal muscle spasms would be most significant when taking the musculoskeletal history of <u>older adults.</u>
This is because older adults often get up at night due to pain and cramps in their bodies, because their muscles are spasming from time to time. The other options, adolescents, infants, and children, as well as middle adulthood, do not experience these problems as much, which is why they wouldn't be suitable for this research.