Explanation:

- The sentence discusses choosing a variety of foods over a period of time to ensure nutritional balance.

- Option 1: "complete" - This does not fit the context as it suggests finishing something rather than spreading out choices.

- Option 2: "between" - This implies choosing two things, rather than a range over time. Doesn’t apply well here.

- Option 3: "throughout" - Fits perfectly as it means during the whole week, aligning with the idea of varying food choices over time.

- Option 4: "every" - It suggests a repetitive or constant action but doesn't fit the context of variety over time.

By selecting "throughout," the sentence conveys that one should vary food choices during the week to ensure a balanced nutrient intake.