The Molecular Basis of a Gene Was Not Known Until

The molecular basis of a gene was not known until:

A) observed in a microscope by the Austrian monk,Gregor Mendel.
B) deduced rather than observed by the naturalist,Charles Darwin.
C) discovered during the 20th century when the electron microscope was invented.
D) observed in the sex cells of eels by Sigmund Freud.
E) deduced rather than observed by Gregor Mendel as a result of his experiments with garden peas.