What is a trait?
A. Differences between generations
B. Similarity between generations
C. Differences between different individuals
D. Both (A) and (B)

Hint: Trait is a characteristic feature expressed by a gene. Examples are axial position of flower, tall height, green color of pod, yellow color of cotyledon/seed. Trait is a character or feature of an organism. It can be a single feature or calculable measurement of an organism. Important traits for genetic analysis are present in different forms in different animals. Trait, which is visible, is the end product of many biochemical and molecular processes.

Complete answer
Different forms of a character are called traits. Trait is influenced by both paternal and maternal DNA. Traits pass on to subsequent generations. Traits in different generations are expressed individually. Dominant and recessive are the two types of traits. Recessive trait is suppressed by the dominant trait.
Genes are present in DNA, which are transferred from one generation to another. Some traits of offspring and parents are similar. When genes or chromosomes cross over, variation occurs between different individuals. Traits’ expression depends on the amount of genes.
Option A Differences between generations: Not only differences but also similarities between generations occur as traits.
Option A is not correct
Option B Similarity between generations: Not only similarities but also differences between generations occur as traits.
Hence, Option B is not correct
Option C Differences between different individuals: Individual difference is not a trait.
So, Option C is not correct
Option D Both (A) and (B): Both similarities and differences between generations are traits.
Option D is correct

So, the correct answer is Option D

Note:
Similarity in trait is white-tailed deer in Pennsylvania: The deer have similar coat color with little variation. Variation in biodiversity is caused by differences between traits. Differences are also involved in the process of evolution. Traits are physical characteristics like eyesight, color patterns, body shape, length and width. Traits expressed as physical appearance are phenotype. Genetic contribution of the trait is genotype.