Veins have all of the following characteristics: (choose 4) A)Large lumen (space inside the vessel)
B) Thick walls
C) valves
D) small lumen (space inside the vessel)
E) thin walls
F) one cell thick
G) low blood pressure

they float because they are less dense than the water itself

something denser than water, like a rock, will sink to the bottom

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.