A two-trait occurs when an individual has two dominant alleles but it is not possible to determine if that individual is homozygous dominant or heterozygous, thus that individual is crossed with an individual who is homozygous recessive for both traits.

This statement refers to Test Cross.

Explanation:

Generally a Test cross involving an individual with a homozygous recessive trait. When a single trait is being studies, a test cross is a cross between an individual with the dominant phenotype but of unknown genotype (either homozygous or heterozygous) with a homozygous recessive individual. If the unknown is heterozygous for a trait, then approximately half of the offspring will display the recessive phenotype. If all the offspring carry dominant phenotype, Then the unknown genotype is homozygous.