The correct answer is: A. specific heat.
Specific heat is the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius. It is a measure of how much a substance resists changes in temperature.
Thermal capacity is the amount of heat required to raise the temperature of a given system by one degree Celsius. It is equal to the product of the specific heat of the system and its mass.
Water equivalent is the mass of water that would absorb or release the same amount of heat as the system under consideration. It is equal to the specific heat of water times the mass of the system.
The answer to the question is A. specific heat.