Answer:
C (All white offsprings)
Step-by-step explanation:
Feather colour in budgies is coded for by two genes (Y and B). The allele Y is dominant over the allele y in the first gene while the allele B is dominant over the allele b.
In a combined state of the two genes;
1. When either of both genes contains a dominant allele, the phenotypic characteristics (feather colour) will be green i.e. YYBB, YyBB, YYBb, YyBb genotypes
2. When both alleles of gene Y are recessive (yy), and one or two of the alleles of gene B are dominant (Bb, BB), the phenotypic characteristics will be blue i.e. yyBB, yyBb genotypes
3. When both alleles of gene B are recessive (bb) and one or two of the alleles of gene Y are dominant (Yy, YY), the phenotypic characteristics will be yellow i.e. Yybb, YYbb genotypes
4. When both alleles of gene Y and B are both recessive (y and b), the phenotypic characteristics will be white i.e. yybb genotype
In this case where a green budgie is crossed with a blue budgie, meaning that, a budgie with either of the genotypes YYBB, YyBB, YYBb, YyBb is crossed with a budgie with either genotypes yyBB, yyBb
Both parents contains genotype that have at least one dominant allele for both genes, therefore, their offsprings cannot have all their alleles recessive.
Since white feather colour will only be phenotypically expressed if both alleles in the two genes are homozygous recessive, then all offsprings cannot have all white feathers (yybb).