The output of a 2-input multiplexer is connected back to one of its inputs as…

Answer: D Latch

Why this is a D latch:

• When the select S = 1, the multiplexer chooses the external data input and passes it to the output (the latch is transparent).

• When the select S = 0, the multiplexer selects the feedback path (the output fed back to the input), so the output retains its previous value (the latch holds).

This pass-or-hold behavior is the defining characteristic of a level-sensitive D latch (enable = S). It is not an edge-triggered D flip-flop, nor a combinational circuit like a half-adder or a demultiplexer.