Final answer:
The best nursing intervention for preventing falls in older adults due to age-related changes is to encourage slow transitions from a supine to an upright position.
Step-by-step explanation:
The nursing intervention that best demonstrates an understanding that older adults are at increased risk for falls because of normal age-related changes is c. Encouraging the patient to rise from a supine position slowly. This intervention directly addresses the physiological changes that occur with aging such as decreased muscle strength, slower reflexes, and potential orthostatic hypotension, which can all contribute to instability and increased fall risk upon rising too quickly. In contrast, speaking in a loud voice, turning on bright lights, and advising to avoid exercising may be beneficial for certain individuals but do not universally address the fundamental age-related changes that increase the risk of falls.