Final answer:
Possible mechanical exfoliation methods involve physical means to remove material from the surface.
Step-by-step explanation:
The possible mechanical exfoliation methods are: (b) by heating, hammering, and spinning it in an external magnetic field, (c) by hammering, heating, and rubbing with cloth, and (d) by cooling, submerging in water, or rubbing with cloth. These methods involve physical means to remove material from the surface, such as heat, hammering, spinning, rubbing, or submerging.
The exception would be method (a), which is not listed in the question, but it would be an incorrect answer as it is not one of the given options.