Which best describes the process by which ultrasounds images are made?
low-frequency sound waves are generated by a machine and refracted off of objects, creating echoes that are processed into images.

high-frequency sound waves are generated by a machine and refracted off of objects, creating echoes that are processed into images.

high-frequency sound waves are generated by a machine and reflected off of objects, creating echoes that are processed into images.

low-frequency sound waves are generated by a machine and reflected off of objects, creating echoes that are processed into images.

In the united states there are strict fishing seasons and limits, but not all countries enforce similar laws. in bangladesh there are few if any fishing restrictions. what might be the reason for less restrictions in smaller countries like bangladesh? a) the united states is the only country worried about overfishing. b) the united states wants to limit the supply of fish to increase the price. c) bangladesh and smaller countries have an unlimited supply of fish in their coastal waters. d) small countries, such as bangladesh, are practicing subsistence fishing, taking only the fish needed to survive.