Heart muscles contract and relax. What is the most important effect of this action on the human body?
O A. Blood is pushed through vessels.
B. The heart beats rhythmically.
C. The heart gets needed exercise.
D. Energy is generated for other organs.

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Which statement correctly describes other ways in which nebulae and stars are different? a. a star always has a higher density than a nebula. b. stars can form inside a nebula but a nebula can never be produced by any star. c. stars can never form inside a nebula but a nebula can be produced by any star. d. a nebula always has a higher density than a star. reset submit