The backbone is made up of many small bones called

The backbone is not a single bone, but a column of drum-shaped bones called vertebrae (singular, vertebra). There are 33 vertebrae altogether, although some of these join together as the body grows. The vertebrae are separated by disks of rubbery material called cartilage. Cartilage is very important because it cushions the bones when you run or jump.  

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i think the answer is b.

hope it