Context: This passage describes the iridescent scales trait in bettas:
A betta, or Siamese fighting fish, is a popular aquarium pet. Many bettas have shiny iridescent scales, which contain tiny crystals that reflect light. These crystals cause the fish's color to look slightly different when seen from different angles. Some bettas are covered in mostly iridescent scales. Other bettas have mostly plain, non-iridescent scales.
In a group of bettas, some individuals have mostly iridescent scales and others have mostly plain scales. In this group, the gene for the iridescent scales trait has two alleles. The allele for mostly iridescent scales (I) is dominant over the allele for mostly plain scales (i).
This Punnett square shows a cross between two bettas.
What is the expected ratio of offspring with mostly plain scales to offspring with mostly iridescent scales? Choose the most likely ratio.
A. 4:0
B. 0:4
C. 2:2
D. 1:3
E. 3:1
Pick the correct answer from the listed options and provide the letter of the selected option.

D