Meaning: 'Lead' means to guide or to result in a particular outcome, in this case, a healthy life.

Wrong options:

• synchronize: 'Synchronize' means to occur at the same time or rate, which does not fit the context of animals living healthy lives.
• quantify: 'Quantify' means to measure or express the amount of something, which does not relate to the ability of animals to live healthily.
• contain: 'Contain' means to hold or include something, which does not fit as it does not describe the action of leading a healthy life.
• enrich: 'Enrich' means to improve or enhance the quality of something, which does not directly relate to the concept of leading a healthy life.
• order: 'Order' means to arrange or request something, which is not relevant to the context of animals living healthily.

Correct answer: contain

Explanation: The verb 'contain' is appropriate here as it indicates that the diets must include essential nutrients. This aligns with the grammatical structure and the context of ensuring that the diets are nutritionally adequate.

Meaning: 'Contain' means to hold or include necessary components, in this case, essential nutrients.

Wrong options:

• synchronize: 'Synchronize' does not fit as it refers to timing rather than the inclusion of nutrients in diets.
• lead: 'Lead' is not suitable here as it does not convey the idea of including necessary nutrients.
• quantify: 'Quantify' means to measure, which does not relate to the requirement of including nutrients in the diets.
• enrich: 'Enrich' implies improving quality but does not specifically indicate the necessity of including essential nutrients.
• order: 'Order' does not relate to the context of dietary requirements and is irrelevant here.

Correct answer: quantify

Explanation: The verb 'quantify' is suitable as it refers to the action of measuring the environmental impact, which is the focus of the researchers' study. This aligns with the context of assessing changes in pet diets.

Meaning: 'Quantify' means to measure or express the amount of something, particularly in a numerical way.

Wrong options:

• synchronize: 'Synchronize' does not fit as it refers to timing rather than measuring impacts.
• lead: 'Lead' is not appropriate here as it does not relate to the action of measuring or assessing.
• contain: 'Contain' does not fit as it refers to holding or including something, not measuring impacts.
• enrich: 'Enrich' means to improve quality, which does not relate to the act of measuring environmental impacts.
• order: 'Order' is irrelevant as it pertains to arranging or requesting rather than measuring or quantifying.