Which one of the following is correct? a)- movement of dislocations is not the primary mechanism of plastic behavior in polymers. b)- interstitial diffusion is common when diffusing species has about the same size as host atoms. c)-fick's first law adequately describes the solutions to problems relating to non-steady state diffusion. d)-secondary bonds can be stronger than primary bonds.

To save energy, the air supply to a 2000 ft office has been shut off overnight and the room temperature has dropped to 40°f. in the morning, the thermostat is reset to 70°f and warm air at 120 f begins to flov in at 200ft'/min. the air is well mixed within the room, and an equal mass flow of air at room temperature (changing with time) is withdrawn through a return duct. the air pressure is nearly 1 atm everywhere. ignoring heat transfer with the surroundings and kinetic and potential energy effects, estimate how long it takes for the room temperature to reach 70°f. plot the room temperature as a function of time.