18) What structure allows a bone to grow in length?C) epiphyseal plate19) The following are major steps in the process of intramembranous ossification.1. Clusters of osteoblasts form osteoid that becomes mineralized.2. Osteoblasts differentiate within mesenchymal connective tissue.3. Spicules of bone radiate out from the ossification centers.4. Mesenchymal cells aggregate.A) 4, 2, 1, 3. 20) Which of the following is formed by intramembranous ossification?21) Endochondral ossification begins with the formation of a(n)A) cartilage model.22) The following are important steps in the process of endochondral ossification.1. Enlarged chondrocytes die.2. Osteoblasts replace calcified cartilage with spongy bone.3. Chondrocytes enlarge and the surrounding matrix begins to calcify.4. Blood vessels invade the perichondrium.5. Perichondrial cells become osteoblasts and produce a thin shell of bone.The correct order for these events isC) 3, 1, 5, 4, 2. 23) Secondary ossification centers occurD) in the epiphyses.24) When production of sex hormones increases at puberty, epiphyseal platesB) become narrower.25) The most abundant mineral in the human body isC) calcium.26) Elevated levels of calcium ion in the blood stimulate the secretion of the hormoneD) calcitonin.27) Osteoclast-activating factor does all of the following, except that itC) is released in large amounts early in life.28) The hormone calcitonin functions toB) decrease the level of calcium ion in the blood.