9. What does energy efficiency mean? A. How much useful work we can get from each unit of energy used
B. How fast the energy can be expended
C. The maximum amount of energy an appliance can use
D. The overall energy use that is tracked throughout time

The answer is A

Explanation:

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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.