DNA is a chain of nucleotides bonded together.  On that chain there are particular portions of it that the sequence of the nucleotide codes for particular proteins; this is known as a gene.  In eukaryotric cells, DNA is coiled around proteins such as histones to form chromatids which when two join at the centre by a centromere to form a chromosome.
        
             
        
        
        
4: a species is a group of interbreeding natural populations that are reproductively isolated from other such groups. Process of Speciation. The process of speciation is a 2 stage process in which reproductive isolating mechanisms arise between groups of populations.
 
        
             
        
        
        
D) would be the answer
Why? when using a scientific method you don't want to choose another thing do you?