Which statement describes the work of Gregor Mendel?
A. He developed some basic principles of heredity without having knowledge of chromosomes. B. He developed the microscope for the study of genes in pea plants. C. He explained the principle of dominance on the basis of the gene-chromosome theory. D. He used his knowledge of gene mutations to help explain the appearance of new traits in organisms. E. He studied the beaks of finches which helped him to develop the theory of evolution by natural selection.