Answer:
B. A gene can take different forms called alleles.
Step-by-step explanation:
Alternative form of a gene are called alleles. As we know that every character of an individual is encoded by genes for example hair color, eye color, nose shape etc.
However, an individual contains only two alternative forms of a certain gene for a certain trait. For example, for eye color there can be only two alleles in an individual, one allele he will inherit from father and other from mother. These both alleles are collectively termed to encode single trait and known as a gene.
The alleles are present on same location on chromosome. Alleles should not be confused with gene because they should just be taken as same thing having two forms, for example there is a gene for eye color in a person.That person received the gene of blue eyes from father and brown eyes from mother. Therefore, that person contains two alleles not two genes. Because one gene is for one trait.
Please see figure for enhanced understanding.
Hope this helps!