Below is a text with blanks. Click on each blank, a list of choices will appear. Select the appropriate answer choice for each blank.
下面的文本有一些空格。点击每个空格会出现一组选项，请为每个空格选出最合适的答案。
Bones are extremely strong. One of their functions is to protect organs. For example, the skull protects the brain and forms the shape of the face. The spinal cord, a pathway for messages between the brain and the body, is protected by the backbone, or spinal column. The ribs form a cage that the heart and lungs, and the pelvis helps protect the bladder, part of the intestines, and in women, the reproductive organs. Joints are where bones meet. They make the skeleton flexible — without them, movement would be impossible. Three kinds of freely movable joints play a big part in voluntary movement: Hinge joints allow movement in one direction, as seen in the knees and elbows. Pivot joints allow a rotating or twisting motion, like that of the head moving from side to side. Ball-and-socket joints allow the greatest freedom of movement. The hips and shoulders have this type of joint, in which the round end of a long bone fits into the hollow of another bone.
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