Solve the following expression using the order of operations: 72 ÷ 8 + 4 × 8 - 20

The expression is $72 \div 8 + 4 \times 8 - 20$.
Following the order of operations (division and multiplication before addition and subtraction):

$$72 \div 8 = 9$$ $$4 \times 8 = 32$$

Now substitute these values back into the expression:

$$9 + 32 - 20$$

Perform addition and subtraction from left to right:

$$9 + 32 = 41$$ $$41 - 20 = 21$$

The value is 21.

The final answer is $\boxed{\text{C. } 21}$.