2 elections will fill the first energy level
Answer:
Muscles work in pairs to move a bone.
Skeletal muscles only PULL in one direction. For this reason they always come in pairs. When one muscle in a pair contracts, to bend a joint for example, its counterpart then contracts and pulls in the opposite direction to straighten the joint out again.
Answer:
a substance made by mixing other substances together.
Explanation:
A mixture is a substance made by mixing two or more substances together.
Chemical properties of an atom are based upon the arrangement of valence electrons (electrons which can be gained, lost, or shared).