What genotypes of two true breeding white flowered strains will produce all white flowered progeny?

The correct choice involves two true-breeding strains that have the same genotype, which in this case is CCpp. True-breeding means that the strains consistently produce offspring with the same phenotype when crossed. In the context of flower color, we can assume that 'C' represents a dominant allele responsible for purple flowers and 'c' represents a recessive allele that leads to white flowers. The genotype CCpp has two dominant alleles (C) responsible for color production but is homozygous for the recessive allele (pp), which generally wouldn’t influence the white flower expression since the flower color expression is controlled by the dominant alleles.

When two true-breeding CCpp plants are crossed, all the offspring will inherit one C allele and one p allele from each parent. Thus, all progeny will have the genotype CCpp, which will express as white flowers due to the presence of the homozygous recessive pp condition, resulting in all progeny showing white flowers.

Understanding this helps clarify why the other options do not yield all white-flowered offspring, as they involve variations in alleles that could lead to different phenotypes depending on the combinations contributed by each parent.