9. Gravity and other forces affect movement within an animal's body. Which system is responsible for the
force that moves blood through the body?
Endocrine system
Circulatory system
Skeletal system
Nervous system

circulatory

Explanation:

Heart is only responsible for generating the pumping force needed to supply blood to each and every corner of the body. As heart is part of circulatory system. The answer is Circulatory system.

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.