Which type of barrier are coughing and sneezing?

Coughing and sneezing are also the part of physical barrier because through coughing and sneezing the microbes are thrown out of the body by physical process. Cough includes many mucus entrapped bacteria in it. Therefore the right answer is d. physical.

Explanation:

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.