True-breeding pea plants always b
produce offspring with only one form of a trait.
produce offspring with either form of a trait.
are heterozygous.
are pollinated by hand.
d

When a single trait is being studies, a test cross is a cross between an individual with the dominant phenotype but of unknown genotype (homozygous or heterozygous) with a homozygous recessive individual. If the unknown is heterozygous, then approximately 50% of the offspring should display the recessive phenotype.

Explanation:

a compound light microscope is used to magnify objects in steps.  

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