Problem: What is the missing first step of the following process: - As the plates move, they exert a great force - When the force is large enough, the crust breaks - The stress is released as energy - The energy moves through the Earth in the form of waves - We feel the earthquake -

A: Plates on the Earth's crust move slowly past each other

Problem: What is the missing first step of the following process: - The lungs have a series of smaller and finer tubes and sacs - Air reaches the smallest and finest air sacs called alveoli - Oxygen travels from the alveoli into the blood - Oxygen-rich blood is carried to the heart - Oxygen-rich blood is pumped throughout the body by the heart - Cells take in the oxygen rich blood and release carbon dioxide rich blood - The carbon dioxide rich blood travels to the lungs - Carbon dioxide travels through the throat and is exhaled.

A: Air enters the nose or mouth and travels through the windpipe into the lungs

Problem: What is the missing first step of the following process: - The star does not have enough mass to become a neutron star - The star goes through a change in its core and bonds helium to carbon and oxygen - The star becomes a red giant - A mass of carbon and oxygen builds up in the center of the star - The star sheds its outside layers and becomes a nebula - The star leaves behind the core which becomes a dwarf star.

A: A star forms

Problem: What is the missing first step of the following process: - Oxygen moves from the lungs into the bloodstream - Air is pushed through the vocal chords - A person talks - Other air is pushed out of the lungs into the environment.

A:
Air is pulled into the lungs