What Made the Plant Hybridization Studies Performed by Mendel More

What made the plant hybridization studies performed by Mendel more successful than plant hybridization studies performed by others?

A) Mendel did not use true-breeding organisms because he wanted to assess the inheritance of more than one trait per breeding.
B) Mendel was the first to identify characteristics of pea plants that could be observed as phenotypes.
C) Mendel's understanding of natural selection inspired his methodology to examine the effect of environmental stressors on genetic diversity.
D) Mendel used statistical analysis to analyze the phenotypes he observed.
E) Mendel used qualitative analysis to evaluate the genotypes he observed.