Problem: - The lungs remove oxygen from the air - Oxygen diffuses from alveoli in the lungs to the bloodstream - Hemoglobin in red blood cells attaches to the oxygen - Red blood cells carry oxygen all around the body - Oxygen diffuses into cells from capillaries. What might be the first step of the process?

A: Air goes into the lungs

Problem: - 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. What might be the first step of the process?

A: Air is pulled into the lungs

Problem: - The seeds are dispersed by wind, animals, etc - The seeds reach the ground - Grow into new trees - These new trees produce seeds - The process repeats itself over and over - What might be the first step of the process?

A: A tree produces seeds

Problem: - The water combines with carbon dioxide in the air to form carbonic acid - As the acid is formed, the iron starts to dissolve - Some of the water breaks down into hydrogen and oxygen - The free oxygen and dissolved iron bond together - They form iron oxide, which is rust - What might be the first step of the process?

A:
Water comes into contact with something made of iron