A) The soft substance present inside the bones is called bone marrow.
B) Pivot joint allows the maximum movement in all planes whereas hinge joint allows the least movement in one plane only.
C) The only movable bone in skull is the upper jaw bone.
D) Snakes have hollow bones and birds have flexible backbones.
Correct Answer: A
Solution :Bone marrow is a soft substance present inside the bones and blood cells are made here. Ball and socket joint allows the maximum movement in all the directions. Hinge joint provides back and forth movement in one plane similar to door hinges. Pivot joint allows one bone to rotate over the other. The only movable bone in skull is the lower jaw bone. Birds have hollow bones that make them light weight and help to fly. Snakes have flexible backbones.
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