Final answer:
Option D, 1/8 + 1/8 = 2/8, best represents the addition of the gray part and the striped part in the whole rectangle.
Step-by-step explanation:
The question asks about the addition of the gray part and the striped part in the whole rectangle. The gray part is represented by 1/8 and the striped part is also represented by 1/8. To find the sum, we add the fractions together by adding the numerators: 1/8 + 1/8 = 2/8. Therefore, option D, 1/8 + 1/8 = 2/8, best represents the addition of the gray part and the striped part in the whole rectangle.