Correctly order the following steps of bone growth in length, by placing a 1 by the first step, a 2 by the second step, and so on.


______Calcified cartilage is replaced with bone in the zone of ossification.                   
______Chondrocytes in the zone of proliferation divide by mitosis.                   
______Chondrocytes enter the zone of calcification and die as their matrix calcifies.                   
______Chondrocytes enlarge and cease dividing.