Introduction:
A Pushdown Automaton (PDA) is a theoretical computational model that is used to describe and analyze the behavior of certain types of computer programs. PDAs are similar to Turing Machines (TM) but have an additional stack memory called the auxiliary memory. This auxiliary memory allows PDAs to store and retrieve information in a last-in-first-out (LIFO) manner, which makes them more powerful than finite-state machines but less powerful than Turing Machines.

Explanation:
The given question states that a PDA behaves like a TM when the number of auxiliary memory it has is 2 or more. Let's understand why this answer is correct.

1. PDA with 0 auxiliary memory:
A PDA without any auxiliary memory is equivalent to a finite-state machine (FSM). FSMs have limited computational power and can only recognize regular languages, which are a subset of the languages that can be recognized by TMs. Therefore, a PDA with 0 auxiliary memory cannot behave like a TM.

2. PDA with 1 auxiliary memory:
A PDA with 1 auxiliary memory is more powerful than an FSM but less powerful than a TM. It can recognize context-free languages, which are a larger class of languages than regular languages. However, it cannot recognize all languages that can be recognized by TMs. Therefore, a PDA with 1 auxiliary memory cannot behave like a TM.

3. PDA with 2 or more auxiliary memories:
A PDA with 2 or more auxiliary memories is capable of recognizing all context-free languages, which includes regular languages. In fact, a PDA with 2 auxiliary memories is equivalent to a TM. This is because the stack memory of the PDA can simulate the tape of the TM, and the transition function of the PDA can simulate the transition function of the TM. Therefore, a PDA with 2 or more auxiliary memories can behave like a TM.

Conclusion:
In conclusion, a PDA behaves like a TM when the number of auxiliary memory it has is 2 or more. With 2 or more auxiliary memories, a PDA can recognize all context-free languages and simulate the behavior of a Turing Machine. However, with 0 or 1 auxiliary memory, a PDA is less powerful and cannot behave like a TM.