The answer is DNA because genotype is the genes of an organism and genes = DNA.
Natural selection means that the organisms better adapted to their environment, that is, they have developed the right characteristics/skills/response to the external ambient, have higher chance to survive, making the next generations genetically inherit such acquired surviving characteristics.
These generations will thus have a higher chance of survival, making these species being "naturally selected" as survivors, while those who haven't or are slower in this process, have a higher risk of elimination.
The answer is C) Cloning eliminates the ability to sexually reproduce and provide genetic variability.
In the future, there is no variability in the genes in the clones given that they are the exact copies of the "parent" produce. All should be identical without differences and variations. Although Farmer Brown doesn't want this to happen that's is what he is reluctant to listen to Farmer Green's advice.
It can also be called a column.
