Explain how it is possible for two parents without blue eyes (a recessive trait) to have a child with blue eyes

This would be possible if both parents were carriers of the allele for blue eyes (heterozygous). This means each would have one blue eye allele and one non blue eye allele and as the non blue eye allele is dominant and the blue eye allele is recessive, their phenotypes would follow that of the dominant allele and so they would not have blue eyes. If two people with this genotype were to have a child together, the allele the child receives from each parent is random. If the child happened to inherit the blue eye allele from each parent, they would have two recessive blue eye alleles (homozygous recessive), and therefore would have blue eyes.