What can be inferred from this excerpt is : ( D ) Individuals with favorable variations survive and reproduce.
When the insecticide was sprayed some of the cockroaches survived and continued reproduction due to their resistance to the spray.Therefore it can inferred that although the cockroaches share the same genetic materials, the variations in individuals within the same specie played a role in the survival of some of the cockroaches.
Hence we can conclude Individuals with favorable variations survive and reproduce.
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