Explanation:

A decoder is a combinational logic circuit that converts n inputs to 2^n outputs, where n is the number of input lines. Each input line represents a specific binary value, and the corresponding output line is activated or enabled based on the input combination.

Example:
Let's consider a 2-to-4 decoder with two input lines, A and B. The decoder converts the binary input combination (A, B) into four output lines (Y0, Y1, Y2, Y3). The truth table for this decoder is as follows:
```
A | B || Y0 | Y1 | Y2 | Y3
---------------------------
0 | 0 || 1 | 0 | 0 | 0
0 | 1 || 0 | 1 | 0 | 0
1 | 0 || 0 | 0 | 1 | 0
1 | 1 || 0 | 0 | 0 | 1
```

From the truth table, we can see that each output line corresponds to a unique binary combination of the input lines. For example, when A=0 and B=0, only the first output line (Y0) is activated. When A=1 and B=1, only the fourth output line (Y3) is activated.

Generalization:
In general, a decoder with n input lines will have 2^n output lines. The number of outputs is determined by the number of unique binary combinations that can be formed with n bits. Since each input line can have two possible states (0 or 1), the total number of combinations is 2^n.

Therefore, the correct answer is option C) 2^n.