4. Read these sentences from the article. "Individual layers of ancient sediment form horizontal stripes on the rock. From a few
steps back, the rock wall looks like a cross-section of a giant, stone encyclopedia."
Why might the author have included this description of the rock wall?
A. to explain why the author quotes scientists in the article
B. to demonstrate why the author explains two different methods used to date the rise of
oxygen in the atmosphere
C. to show why the author presents information about different compounds in the article
D. to clarify why the author compares studying a rock formation to studying a book

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when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.

plants absorb water from the soil by osmosis. root hair cells are adapted for this by having a large surface area to speed up osmosis. the absorbed water is transported through the roots to the rest of the plant where it is used for different purposes: it transports dissolved minerals around the plant.