The central canal _____________________.
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   is located within the grey matter of the spinal cord; | 
   
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   contains cerebral spinal fluid; | 
   
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   is a hollow tube that runs the length of the spinal cord; | 
   
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   both alternatives a and b are correct; | 
   
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   all of the above alternatives are correct; | 
   
   
   
   
   
   [Review Part 1 of the tutorial]
   [Review Part 2 (Matching) of the tutorial]