Which of the following pairs have DIFFERENT expressive power?
Just to add.
Expressive power of the following version of Deterministic Turing machine is same
Expressing power of any machine can be defined as the maximum number of languages it can accept..if machine $M_1$ can accept more languages then $M_2$ then we can say that expressing power of $M_1$ is greater then $M_2$.
Answer is B.
(B) Deterministic push down automata (DPDA) and Non-deterministic push down automata (NPDA)
In rest of the options both machine are equivalent in power.
In given option all are same expressive power but NPDA and DPDA have different expressive power
So option B is true.