A full adder is a combinational circuit that performs addition of three bits: two inputs (A and B) and a carry input (Cin). The output of a full adder consists of two bits: a sum (S) and a carry output (Cout). Therefore, a 3-bit full adder is a circuit that can perform addition of three sets of three bits.

The inputs of a 3-bit full adder are the three sets of three bits: A0, B0, Cin0, A1, B1, Cin1, A2, B2, and Cin2. Each set consists of two bits for the numbers being added (A and B) and one bit for the carry input (Cin).

To explain the answer in detail, let's break it down into headings and key points:

1. Combinational Inputs:
- A combinational input is a term used to describe an input that affects the output of a combinational circuit.
- In the case of a full adder, the combinational inputs are the three sets of three bits: A0, B0, Cin0, A1, B1, Cin1, A2, B2, and Cin2.

2. Three Sets of Three Bits:
- Each set of three bits represents the numbers being added (A and B) and the carry input (Cin) for a particular bit position.
- In a 3-bit full adder, there are three sets of three bits: A0, B0, Cin0 for the least significant bit (LSB), A1, B1, Cin1 for the middle bit, and A2, B2, Cin2 for the most significant bit (MSB).

3. Total Combinational Inputs:
- To calculate the total number of combinational inputs, we need to count the number of individual bits in all the sets.
- In a 3-bit full adder, each set consists of two bits for the numbers being added (A and B) and one bit for the carry input (Cin).
- Therefore, the total number of combinational inputs is 2 bits + 2 bits + 2 bits + 1 bit + 1 bit + 1 bit + 1 bit + 1 bit + 1 bit = 12 bits.

4. Answer Explanation:
- The correct answer is option D, which states that a 3-bit full adder contains 8 combinational inputs.
- This answer is incorrect because a 3-bit full adder consists of three sets of three bits, resulting in a total of 9 bits, not 8 bits.
- The correct answer should be option C, which states that a 3-bit full adder contains 6 combinational inputs.

In conclusion, a 3-bit full adder contains 6 combinational inputs: A0, B0, Cin0, A1, B1, and Cin1. Each set of inputs consists of two bits for the numbers being added (A and B) and one bit for the carry input (Cin).