Explanation:
In genetics, the first filial generation (F1) refers to the offspring produced by crossing two purebred parents. The characters that appear in the F1 generation can be classified as either dominant or recessive.

Dominant Characters:
Dominant characters are traits that are expressed in the presence of a single copy of the gene. In other words, if an individual inherits a dominant allele for a particular trait, that trait will be observable in their phenotype. Dominant characters mask the expression of recessive characters.

For example, if we consider a cross between a purebred tall pea plant (TT) and a purebred short pea plant (tt), where the allele for tallness (T) is dominant over the allele for shortness (t), all the offspring (F1 generation) will be tall (Tt). In this case, the dominant character is the tallness of the plants.

Recessive Characters:
Recessive characters, on the other hand, are traits that are only expressed if an individual inherits two copies of the recessive allele. If an individual inherits a dominant allele for a particular trait, the recessive allele will be masked and not expressed in their phenotype.

In the previous example, although the F1 generation plants are all tall, they still carry the recessive allele for shortness (t). If two plants from the F1 generation are crossed with each other (Tt x Tt), their offspring (F2 generation) will have a phenotypic ratio of 3 tall plants (TT or Tt) to 1 short plant (tt). This is because the recessive trait for shortness is only expressed in individuals with two copies of the recessive allele (tt).

In summary, the characters that appear in the first filial generation can be classified as dominant or recessive based on their expression in the presence of one or two copies of the respective alleles. In this context, the correct answer is option B: dominant characters.