单选题

干：The ovaries produce ____ and release sex hormones estrogen and progesterone.
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单选题 干：Joints make the skeleton flexible. Without them, ____ would impossible.
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单选题 干：____ is large lymphoid organ, lying in the human body to the left of the stomach below the diaphragm.
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单选题 干：The ____ system breaks down the food you eat.
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单选题 干：Our muscles alternately ____ and relax as we move our limbs back and forth.
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单选题 干：The ____ is part of the digestive system and also the respiratory system.
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单选题 干：When the ____ is injured, the exchange of information between the brain and other parts of the body is disrupted.
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单选题 干：One way the immune system attacks foreign substances in the body is by making large numbers of ____.
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单选题 干：____ is male sex hormone that is important for sexual and reproductive development.
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