Final answer:
The allele b is being selected against and is decreasing in frequency.
Step-by-step explanation:
Based on the data provided, a valid conclusion is that the allele b is being selected against and is decreasing in frequency. This conclusion can be drawn because the number of individuals exhibiting the recessive phenotype is decreasing over several generations. Since the dominant allele B exhibits complete dominance over the recessive allele b, the decrease in individuals with the recessive phenotype suggests that individuals with the dominant phenotype have a higher fitness and are more likely to survive and reproduce.