As a long bone develops, the point where osteoblasts first replace calcified cartilage with spongy bone becomes the from which further development proceeds.

a) primary ossification center

b) metaphysis

c) periosteum

d) secondary ossification center

e) epiphyseal line

A) primary ossification center

Explanation:

Endochondral ossification refers to the gradual replacement of a cartilage model with a bone. The primary ossification center represents the region where bone tissue gradually replaces most of the cartilage model. The deposition of the bone extracellular matrix over the remnants of calcified cartilage is done by osteoblasts. It results in the formation of spongy bone trabeculae. Primary ossification spreads from the central location toward both ends of the cartilage model.

c. earths continental crust is thicker than its lithosphere.

because, the lithosphere is the outermost layer of the earth/ 100 km thick and is defined by its machanical properties.the lithosphere contains oceanic and continental crust that varies in age and thickness across locations and geologic time. the lithosphere is the coolest layer of the earth in terms of temperature. the term lithosphere should not be confused with the use of "geosphere" which is used to indicate all of earth systems, including the atmosphere, hydrosphere   and biosphere. the surface of the earth can be divided into the continental crust and the oceanic crust.   the continental crust is made mostly of granite while the oceanic crust is made of basalt. the average thickness of the continental crust is 25 miles and the average thickness of the oceanic crust is 5 miles.   three types of rock, igneous, sedimentary, and metamorphic, make up the surface of the earth. that's why 3 option is preferable.