Answer: Having the most offsprings
Explanation:
Natural selection is the differential survival and reproduction of the some of the members of the population those who have benefit of survival under the adverse conditions.
Such members of the population will survival and reproduce more offsprings than others this can be considered as fitness or survival of the fittest.
cardiotonic is a drug or substance having a tonic effect on heart.
The answer for what if you don't have anything on here.?