The correct answer is (A) Chromosomes.
The color of the horse coat is determined by chromosomes. The genes present on the chromosomes is responsible for the coat color of horse. The dominant coat color of the horse is transferred to the horse from its parents.  This is inherited pattern and the coat color can be black, white, brown, etc. 
 
        
                    
             
        
        
        
Rose bush because not many animals eat rose bushes
        
                    
             
        
        
        
How does a new hypothesis replace an older explanation of something in the natural world? To understand this let us look at one of the classical example of geocentric theory and heliocentric theory. The geocentric theory states the Earth is at the centre of the solar system and the Sun, Moon, and all the other planets revolve around it. This ancient theory failed to explain the phenomenon like the phases of Moon, solar eclipse and lunar eclipse. The modern heliocentric theory which states that the Sun is at the centre of solar system, and all the planets including the Earth revolve around it. This theory was able to explain all the phenomenons unlike the geocentric theory. Hence the heliocentric theory replaced the geocentric theory.
 
        
             
        
        
        
Biology Biology Biology
I don’t what else to say
        
                    
             
        
        
        
<span>Opaca and Marginal zone stays outer and does not move during chick gastrulation,
The zone opaca is a thick fringe ring comprising of more than one cell, it is joined to the germ wall. The Marginal zone lies at the fringe between the range opaca and the region pellucida</span>