Which of the following is a common assistive device?

A common assistive device is specifically designed to aid individuals in improving their mobility and independence, particularly those who have difficulty walking or maintaining balance. A walker serves this purpose effectively as it provides support and stability, allowing users to move safely and confidently. This device is particularly beneficial for elderly individuals, those recovering from surgery, or patients with certain disabilities, helping to enhance their quality of life.

On the other hand, other options like a surgical chair, ultrasound machine, and ECG machine, while essential within the medical field, do not fall under the category of assistive devices meant for personal mobility assistance. A surgical chair is used in operating rooms for patient positioning, while ultrasound and ECG machines are diagnostic tools used for medical imaging and monitoring heart activity, respectively. These devices serve critical functions in healthcare but do not provide the same kind of mobility support that a walker does.