Answer:
The average speed for the entire run is 12 km/h.
Explanation:
The average speed is given by the following equation:

Where:
: is the total distance
: is the total time
If during the first hour, they ran a total of 13 kilometers and then, they ran 5.0 kilometers during the next half an hour we have:


Hence, the average speed is:

Therefore, the average speed for the entire run is 12 km/h.
I hope it helps you!
I believe scattering is what occurs when light essentially changes direction after colliding with small particles of matter.
Answer: B. A gravitational field
Explanation:
Surrounding earth is gravitational field. Gravitational field is a region of space were gravitational force can be felt and gravitational force is the gravitational pull on the surface of the earth. The presence of this gravity is what allow us to be able to walk freely without falling. It also make us jump up and be able to land back on the ground. Assuming there are no force of gravity in the surface of the earth, there won't be any possibility of landing back on the ground after jumping.
Disposing of hazardous waste in a labeled container