1-to-4 Demultiplexer:
A 1-to-4 demultiplexer is a digital circuit that takes one input signal and selects one of the four output channels based on the control signals. It is the opposite of a multiplexer, which takes multiple input signals and selects one output channel.

Working of a 1-to-4 Demultiplexer:
A 1-to-4 demultiplexer has one input line and four output lines. The number of select lines determines the number of output channels and the corresponding decoder logic. Each select line enables one of the four output channels.

Number of Select Lines:
The number of select lines required in a 1-to-4 demultiplexer can be determined by the formula 2^n, where 'n' is the number of select lines. In this case, we have four output channels (2^2 = 4), so the number of select lines required is '2'.

Explanation:
To understand why the correct answer is option 'A' (2 select lines), let's consider the truth table of a 1-to-4 demultiplexer.

Truth Table:
| S1 | S0 | D0 | D1 | D2 | D3 |
|----|----|----|----|----|----|
| 0 | 0 | I | 0 | 0 | 0 |
| 0 | 1 | 0 | I | 0 | 0 |
| 1 | 0 | 0 | 0 | I | 0 |
| 1 | 1 | 0 | 0 | 0 | I |

In the truth table above, 'S1' and 'S0' are the select lines, 'I' is the input signal, and 'D0', 'D1', 'D2', and 'D3' are the output signals.

Analysis:
From the truth table, we can observe that:
- When 'S1' and 'S0' are both '0', the input signal 'I' is transmitted to the output line 'D0'.
- When 'S1' is '0' and 'S0' is '1', the input signal 'I' is transmitted to the output line 'D1'.
- When 'S1' is '1' and 'S0' is '0', the input signal 'I' is transmitted to the output line 'D2'.
- When 'S1' and 'S0' are both '1', the input signal 'I' is transmitted to the output line 'D3'.

Conclusion:
From the above analysis, it is clear that with two select lines, we can control the selection of one of the four output channels. Thus, the correct answer is option 'A' (2 select lines) for a 1-to-4 demultiplexer.