How do I correctly answer the questions below?

Both Darwin and Wallace failed to understand an important aspect of natural selection.  They realized that plant and animal populations are composed of individuals that vary from each other in physical form.  They also understood that nature selects from the existing varieties those traits that are most suited to their environment.  If natural selection were the only process occurring, each generation should have less variation until all members of a population are essentially identical, or clones of each other.  That does not happen.  Each new generation has new variations.  Darwin was aware of this fact, but he did not understand what caused the variation.  The first person to begin to grasp why this happens was an obscure Central European monk named Gregor Mendel  .  Through plant breeding experiments carried out between 1856 and 1863, he discovered that there is a recombination of parental traits in offspring.  Sadly, Darwin and most other 19th century biologists never knew of Mendel and his research.  It was not until the beginning of the 20th century that Mendel's pioneer research into genetic inheritance was rediscovered.  This was long after his death.   He never received the public acclaim that was eventually showered on Darwin during his lifetime.