Which of the following statements is true?

a) cool air is less dense than warm air.
b) sound does not require a medium for travel.
c) magnetism is caused by the spinning motion of electrons.
d) electricity flows from positive to negative areas.

In what layer of the sun is energy transfers between atoms

Which phrase is the best summary of the model shown? a. the transfer of the sun's energy through trophic levels b. a series of aerobic and anaerobic reactions c. a transformation of light energy into chemical energy d. the breakdown of food molecules

What were the main components of earth’s earliest atmosphere? oxygen and ammonia hydrogen and helium oxygen and nitrogen hydrogen and nitrogen