Which statement best describes a keystone species? O A. It is the largest population in the community.
B. It occupies the highest trophic level in the
community
C. Its absence would affect many organisms in the
community.
O D. It is the largest animal in the community.

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.