A circle graph would be most useful for illustrating which of the following?

A circle graph, commonly known as a pie chart, effectively displays proportions of a whole, making it particularly useful for illustrating percentages. In the context of the provided choices, the percentage of total gross sales contributed by each product represents part-to-whole relationships, where each product’s contribution can be visually compared to the total gross sales.

This visual representation allows stakeholders to quickly grasp how much of the total sales each product represents, highlighting dominant products and potentially revealing areas for improvement. The remaining options, while they involve numerical data, do not emphasize proportional relationships in the same way. Annual profit, market share among competitors, and growth rates over time are more suited for line graphs, bar charts, or other forms of graphical representation that can accurately depict trends or comparisons across non-proportional data.