Which of the following is an example of two or more body systems interacting to maintain homeostasis?

When body temperature is high, signals from the brain cause increased blood flow to the skin.
When calcium levels in the blood are low, hormones cause calcium to be released from bones.
When too much salt is consumed, it is filtered out of the blood by the kidneys and excreted.

elements make up everything, and they combine to make compounds.

the answer is c

ca has a crystalline lattice with positive ions (since it is a metal, metals are positively charged) and electrons flow freely in its structure since the ca atoms have a large nuclear radius so the electrons are not tightly held, therefore the electrons can flow freely since they are not being highly attracted by the nucleus. moreover, one of the properties of metals are that they are conductors of electricity, thus proving ca is the element.