Answer: B. the physical appearance of a trait
Step-by-step explanation:
The allelic combination of an organism is called as genotype. The expression of any one of the alternative allele in an organism will lead to the expression of a particular trait in organism's morphology, physiology, and behavior. The expression of these traits are observable in an organism. The expression of such observable traits is called as phenotype.
On the basis of the above explanation, B. the physical appearance of a trait is the correct option.