Why are two balls connected by a spring a good model for two atoms connected by a chemical bond?

A) The magnitude of the force one atom exerts on another is proportional to the stretch or compression of the bond between them.

B) If the two atoms get farther apart than the equilibrium interatomic distance, they attract each other.

C) Each spring represents a real microscopic coiled metal wire that connects two adjacent atoms.

D) If the two atoms get closer together than the equilibrium interatomic distance, they repel each other.

Note: I already tried A B C and A B and A D and none of these combinations are correct.

Air enters a gas turbine with two stages of compression and two stages of expansion at 100 kpa and 17°c. this system uses a regenerator as well as reheating and intercooling – the intercooler returns the air to the inlet temperature. the pressure ratio across each compressor is 4 ; 300 kj/kg of heat are added to the air in each combustion chamber; and the regenerator operates perfectly while increasing the temperature of the cold air by 20°c. determine the system’s thermal efficiency. assume isentropic operations for all compressor and the turbine stages and use constant specific heats at room temperature. (0.378)