Fact 1: Cells secrete acids and bases to maintain the proper pH for enzymes to work.  Fact 2: Most human enzymes work at a optimal pH of 7.4, but other enzymes work at many different pH ranges.  Given the two facts above, cells secrete acids and bases to maintain what?
OPTIONS:
- Chemical energy
- resistance
- increases a body's strength
- To keep their body heat.
- most human enzymes
- aerobic capacity
- allow growth
- temperature
most human enzymes
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Fact 1: The digestive system breaks food into nutrients for the body.  Fact 2: Another nutrient to be concerned with is iron.  Given the two facts above, what does the digestive system break food into for the body?
OPTIONS:
- sugar
- fatty
- iron
- lipids
- edible
- liquid
- matter
- Energy
iron
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Fact 1: Muscles can only contract.  Fact 2: Muscles in the upper arm called biceps are used to flex the arm.  Given the two facts above, what can only contract?
OPTIONS:
- nerves
- Epidermis
- the skin
- strong
- biceps
- Bend
- lungs
- forces
biceps
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Fact 1: Carbon may be stored in sedimentary rock for millions of years.  Fact 2: Limestone is a type of sedimentary rock.  Given the two facts above, where might carbon be stored for million of years?
OPTIONS:
- In sediment
- stomach
- limestone
- refrigerator
- weathering
- loose dirt
- Earth
- body water

limestone
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