A low area of land often forms between hills or mountains. This low area is
called a valley. Which of the following might cause a valley to form?
A. Waves from the ocean
B. Basaltic lava flow from fissures
C. Soil creep from freezing and thawing
D. Erosion by a stream

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.

c should be the answer

plato users:

d.  

there was a variety of food available on island x, but there were only large seeds and nuts on island y.