The 'pure line' theory was proposed by

Answer: Option B

The 'pure line' theory was proposed by Johannsen.
Wilhelm Johannsen was a Danish pharmacist, botanist, plant physiologist, and geneticist. He is best known for coining the terms gene, phenotype, and genotype, and for his 1903 "pure line" experiments in genetics.
A pure line is the progeny of a single self-fertilized homozygous plant.