Assessment Item 29 close window

Which of these is an example of feedback in a biological system?
 
Fake Radio Button   A     the movement of salts from cells into the bloodstream
Fake Radio Button   B     the release of insulin into the bloodstream when blood sugar increases
Fake Radio Button   C     the decrease in oxygen levels in the blood after vigorous exercise
Fake Radio Button   D     the use of energy when muscles contract
 
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