Why is most space exploration accomplished with spacecraft that do not have astronauts on board

Describe how the motion of a spring being pushed forward and backward is similar to the motion of air particles in a sound wave.

Which of these is the best way to manage a natural resource

This event is the result of a sudden vertical offset in the ocean floor and is most often the result of plate movement on the ocean floor. it destroys coast lines and coastal settlements. what is the event called that causes this type of physical damage? a. volcano b. tsunami c. landslide d. liqufication pls !