Meaning: 'Incur' means to become subject to something unwelcome or unpleasant as a result of one's own actions, in this case, costs associated with food choices.

Wrong options:

• prove: The verb 'prove' means to demonstrate the truth or existence of something, which does not fit the context of incurring costs.
• degradation: While 'degradation' is relevant to the topic, it is a noun and does not fit grammatically in this verb position.
• variation: 'Variation' is a noun that refers to a change or difference, which does not fit the context of incurring costs.
• shifts: 'Shifts' is a noun that refers to changes, but it does not convey the action of incurring costs.
• conservation: 'Conservation' is a noun that refers to the act of preserving something, which does not fit the context of incurring costs.

Correct answer: degradation

Explanation: The term 'degradation' is a noun that refers to the deterioration of the soil quality, which fits contextually as it is one of the negative consequences of food choices mentioned in the sentence.

Meaning: 'Degradation' means the process of something being damaged or deteriorated, particularly in terms of environmental quality.

Wrong options:

• incur: 'Incur' is a verb and does not fit as a noun in this context.
• variation: 'Variation' is a noun that refers to differences, which does not specifically relate to the deterioration of soil.
• shifts: 'Shifts' is a noun that refers to changes, but it does not relate to the concept of soil quality deterioration.
• conservation: 'Conservation' is a noun that refers to the act of preserving, which does not fit the context of soil deterioration.

Correct answer: shifts

Explanation: The word 'shifts' is a noun that refers to small changes in food choices. It fits grammatically and contextually as it describes the potential adjustments Americans can make to improve health and environmental outcomes.

Meaning: 'Shifts' means changes or alterations, particularly in the context of food choices.

Wrong options:

• incur: 'Incur' is a verb and does not fit as a noun in this context.
• degradation: 'Degradation' is a noun that refers to deterioration, which does not relate to changes in food choices.
• variation: 'Variation' is a noun that refers to differences, but it does not specifically imply the small changes suggested in the context.
• conservation: 'Conservation' is a noun that refers to preservation, which does not fit the context of making changes in food choices.