Blocks A, B, and C are brought pairwise into thermal contact in an insulated laboratory. After a long time block A is observed to be in equilibrium with block B, and block B is in equilibrium with block C. Which of the following must also be true?
(a) Block A must be at a higher temperature than block C.
(b) When all three blocks are placed together, block B will absorb heat from block A.
(c) Blocks A and C will be in thermal equilibrium when they are brought into contact.
(d) Blocks A and C will exchange heat until both reach a temperature that is the average of their initial temperatures.