Which statement is an example of a scientific theory? A.
Hummingbirds do not like the color white because they visit other colored flowers more often.
B.
The amount that caffeine affects a person's heart rate differs based on the person's age.
C.
The Earth is the third planet from the Sun and has one moon, which orbits the Earth.
D.
All living organisms are composed of one or more cells, which came from pre-existing cells.

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.

the correct answer is 4) heat and pressure

metamorphic rocks arise from transformation of existing rocks types, in a process called metamorphism. during metamorphism the original rock(prolith) change into metamorphic rock by heating (150-200c) and pressure of more than 1000 bar. the original rock can be sedimentary, igneous, or existing metamorphic rock.