The correct option is B The sugar is in themal equilibrium with the milk.
From the zeroth law of thermodynamics, we can say that, if two objects are in thermal equilibrium with a third object, then they must be in thermal equilibrium with each other.
So in our example, given the coffee and milk are in thermal equilibrium with each other (same temperature).
Also, the sugar is in thermal equilibrium with coffee.
Hence, the sugar will be in thermal equilibrium with milk.
Thus, only option (b) is the correct answer.