Pumping blood in and out of the heart.
Answer: the structure of an atom: At the center of the atom, there is a very small region called the nucleus. This area makes up most of the mass of the atom.
The area around the nucleus is called the electron cloud. This area makes up the majority of the volume of the atom. The electron cloud is mostly empty space.
Explanation: Hope this helps :)
An estuary is an area where a freshwater river or stream meets the ocean. In estuaries, The salty ocean mixes with a fresh water river, resulting in brackish water. Brackish water is someone salty, but not as salty as the ocean. An estuary may also be called a bay, lagoon, sound, or slough.