Answer:
D (Genotype)
Explanation:
A genotype is the genetic make up of an organism i.e. what the genetic material 
of an organism constitutes. Genotype describes the set of genes contained in an organism's genome. According to Mendel, an organism receives two forms of genes called ALLELE for a trait, one from each parent. The genotype of a specific gene coding for a trait is represented by each pair of allele for that trait.
Although the genotype of an organism is outwardly invisible i.e. cannot be seen, but it determines the phenotype of that organism i.e. the outward appearance. For example, if a plant receives T and T alleles coding for tallness, from each parent. The genotype of that plant for the specific height trait will be (TT). Hence, the TT genotype although invisible but controls the tallness of the plant.
 
        
             
        
        
        
Remember that a controlled variable is a variable that stays the same thoughout the experiment.
it wouldn't be a. because two different wires were used
the final length of the wax would be your dependent variable, so it wouldn't be c.
the thermal conductivity is the independent variable so it isn't d.
the original length of the wax was the same for both.
So B is your answer.
        
                    
             
        
        
        
Gene mapping describes the methods used to identify the locus of a gene and the distances between genes. The essence of all genome mapping is to place a collection of molecular markers onto their respective positions on the genome. i hope this helps.
 
        
             
        
        
        
Basically because they either have beating hearts, organs, skeletons, and more that plants and other things do not