Pushdown Automata (PDA):
A pushdown automaton is a finite automaton with an additional stack memory. It is capable of recognizing context-free languages. A PDA uses a stack to store information during the computation.

Turing Machine (TM):
A Turing machine is a mathematical model of a general-purpose computer. It consists of an infinite tape divided into cells, a read-write head that can move left or right on the tape, and a control unit that determines the machine's behavior based on the current state and the symbol being read.

Nondeterministic Finite Automaton (NFA):
A nondeterministic finite automaton is a finite automaton where multiple transitions can be taken from a single state for a given input symbol. It is capable of recognizing regular languages.

Even Palindrome:
An even palindrome is a string that remains unchanged when reversed. For example, "aba" is an even palindrome, but "abc" is not.

Accepting Even Palindromes:
To accept even palindromes over {a, b}, we need a machine that can recognize and accept strings that are even palindromes. This means that the string should be the same when read from left to right and from right to left.

PDA, TM, and NFA for Even Palindromes:
1. PDA: A pushdown automaton can accept even palindromes over {a, b}. The stack can be used to compare the symbols from the left and right ends of the string.

2. TM: A Turing machine can also accept even palindromes over {a, b}. The tape can be used to compare the symbols from the left and right ends of the string.

3. NFA: A nondeterministic finite automaton can also accept even palindromes over {a, b}. The transitions can be defined to handle the comparison of symbols from the left and right ends of the string.

All of the mentioned:
Since all three machines (PDA, TM, NFA) can recognize and accept even palindromes over {a, b}, the correct answer is option 'C' - All of the mentioned.