How many truth table entries are necessary for a four-input circuit?

ANS:D - 16

For 2 inputs: 2^2 = 4 truth table entries..

0 0
0 1
1 0
1 1

For 3 inputs: 2^3 = 2 x 2 x 2 = 8 truth table entries...

0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
1 1 1

Like the same, For 4 inputs: 2^4 = 2 x 2 x 2 x 2 = 16 entries required.

0 0 0 0
0 0 0 1
0 0 1 0
...
...
1 1 1 1