Explanation:

- We have four consecutive odd numbers: a, b, c, d.

- The average of these numbers is 18.

- This means: (a + b + c + d) / 4 = 18.

- Solving, we get: a + b + c + d = 72.

- Since the numbers are consecutive, express them as: a, a+2, a+4, a+6.

- Their sum is: a + (a+2) + (a+4) + (a+6) = 72.

- This simplifies to: 4a + 12 = 72.

- Solving for 'a': 4a = 60, so a = 15.

- Thus, b = 17, c = 19, d = 21.

- The average of b and c is: (b + c) / 2.

- This becomes: (17 + 19) / 2 = 18.

- Option 2: 18