Meaning: 'Place' in this context means a specific position or situation, particularly referring to the initial occurrence of how skin patterns are formed.

Wrong options:

• moment: 'Moment' refers to a brief period of time and does not convey the broader context of a situation or condition as effectively as 'place.'
• instance: 'Instance' implies a particular case or example, which does not fit the idiomatic expression 'in the first place' as well as 'place.'
• phase: 'Phase' suggests a stage in a process, which does not align with the idea of an initial condition or context as intended in this sentence.

Correct answer: by adding

Explanation: The phrase 'by adding' correctly indicates the method through which Alessio and Gupta improved Turing's theory, fitting grammatically as it introduces the action of enhancement in a clear and direct manner.

Meaning: 'By adding' means to include something additional, indicating that they incorporated a new factor into the existing theory.

Wrong options:

• to add: 'To add' suggests an infinitive form that does not fit the grammatical structure of the sentence, which requires a gerund to indicate the method of improvement.
• if added: 'If added' introduces a conditional clause that does not match the definitive action taken by the scientists in this context.
• adding: 'Adding' alone lacks the necessary preposition to indicate the manner in which the improvement was made, making it less clear than 'by adding.'

Correct answer: separating

Explanation: The word 'separating' fits grammatically as a gerund that describes the action of dividing color cells into different areas, which is essential to the explanation of how patterns are formed.

Meaning: 'Separating' means to divide or set apart, indicating that the process involves distinguishing color cells into distinct regions.

Wrong options:

• involving: 'Involving' suggests inclusion rather than the specific action of division, which does not accurately convey the intended meaning in this context.
• dropping: 'Dropping' implies a sudden release or fall, which does not relate to the process of creating patterns through division of color cells.
• eliminating: 'Eliminating' means to remove entirely, which contradicts the idea of organizing color cells into different areas rather than removing them.

Correct answer: crucial

Explanation: The word 'crucial' fits grammatically and contextually as it emphasizes the importance of the new factor in creating animal skin patterns, aligning with the overall sentiment of the sentence.

Meaning: 'Crucial' means extremely important or essential, indicating that this new factor plays a significant role in the formation of patterns.

Wrong options:

• independent: 'Independent' suggests a lack of reliance on other factors, which does not convey the necessary importance of the new factor in the context of pattern creation.
• modest: 'Modest' implies a lack of importance or significance, which contradicts the intended meaning of the new factor being vital for pattern formation.
• favorable: 'Favorable' indicates a positive condition but does not capture the essential nature of the factor as effectively as 'crucial.'