Natural selection is best described as (1 a change in an organism in response to a need of that organism (2 a process of nearly constant improvement that leads to an organism that is nearly perfect (3 differences in survival rates as a result of different inherited characteristics (4 inheritance of characteristics acquired during the life of an organism

(3) differences in survival rates as a result of different inherited characteristics

Explanation:

Natural selection is a driving force for evolution that acts on beneficial variations. Presence of beneficial variations in some members of a population gives them survival advantage. These organisms are able to produce more number of progeny as compared to those who lack those variations. Natural selection favors the organisms having beneficial variations and leads to evolution of better adapted population in time.

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.