Instructions: There are only four members of a family, namely A, B, C and D, and there is only one couple among them. When asked about their relationships, their replies were as follows:
A: “B is my son. D is my mother.”
B: “C is my wife. D is my father.”
C: “D is my mother-in-law. A is my daughter.”
D: “A is my grand-daughter. B is my daughter-in-law.”
Who always speaks the truth?