I suggest you to provide some options, as it's quite difficult to answer your question. Here is your answer: A long bone is covered externally with a sheath called the 
periosteum, whereas the marrow cavity is lined with the <span>
endosteum</span>
. I've attached the illustration to make it clear for you
 
        
        
        
Answer:
Amber is the fossilized resin from ancient forests. Amber is not produced from tree sap, but rather from plant resin. This aromatic resin can drip from and ooze down trees, as well as fill internal fissures, trapping debris such as seeds, leaves, feathers and insects.
 
        
             
        
        
        
It was from nuclear fusion. (Sorry if it’s wrong but I’m pretty sure it’s not!)
        
             
        
        
        
The correct answer is stabilizing selection.
Stabilizing selection is a kind of natural selection in which the mean of the population steadies on a specific non-extreme trait value. This is considered to be the most general process of action for natural selection as the majority of the traits do not seem to vary radically with time.
Stabilizing selection is the reverse of disruptive selection. In spite of preferring individuals with extreme phenotypes, it favors the transitional variants. Stabilizing selection seems to eradicate the more extreme phenotypes, resulting in the reproductive success of the average or norm phenotypes.
This signifies that the most general phenotype in the population is chosen and continues to govern in the coming generations. As the majority of the traits vary slightly with time, stabilizing selection is considered to be the most usual kind of selection in the majority of the populations.