4. A fraction with a numerator of 1 and a denominator that is a natural number greater than 1 is called a unit fraction. If $\frac{1}{8}$ is expressed as the sum of two different unit fractions, then the number of all possible combinations is ( ).
(A) 1 combination.
(B) 2 combinations.
(C) 3 combinations.
(D) 4 combinations.
$\begin{array}{c}4 \\ - \\ C\end{array}$