A new trait that allows a more efficient release of energy from food appears in a fly population. The trait proves beneficial to survival and quickly spreads through the population. Which is the MOST likely origin of the new trait?

A. the mutation of a gene that results in an altered protein

B. the adaptation of a new genes to existing genes in the digestive system

C. the combination of recessive genes in each generation

D. the replication of a gene that produces an increase in RNA

Please help! Will award brainliest (: