Meaning: 'At the same time' means occurring simultaneously or concurrently, highlighting the paradox of being both responsible and reckless.

Wrong options:

• for the time being: This phrase means temporarily or for a limited period, which does not convey the simultaneous nature of the actions described.
• as ever: This phrase suggests continuity or consistency, which does not fit the context of contrasting behaviors.
• in good time: This phrase refers to doing something at the right moment, which does not relate to the simultaneous actions of being clever and reckless.

Correct answer: exploring

Explanation: The word 'exploring' fits grammatically as it indicates an ongoing action of investigation, which is appropriate in the context of the physicians studying the adolescent brain. It also aligns with the context of research and discovery.

Meaning: 'Exploring' means to investigate or examine something in detail, which is what the physicians are doing with the adolescent brain.

Wrong options:

• explaining: This implies making something clear or understandable, which does not capture the depth of investigation suggested in the context.
• exposing: This means revealing something hidden, which does not fit the context of studying the brain's structure and chemistry.
• enumerating: This means listing or counting, which does not align with the idea of in-depth research and understanding.

Correct answer: adult

Explanation: The word 'adult' is the correct choice as it describes the brain's maturity level, contrasting it with the teenage brain. It fits grammatically and contextually, emphasizing the difference between adolescent and adult brains.

Meaning: 'Adult' refers to a fully developed person or brain, highlighting the immaturity of the teenage brain in comparison.

Wrong options:

• ample: This means plentiful or sufficient, which does not relate to the maturity of the brain.
• adulthood: This refers to the state of being an adult, which does not fit grammatically as it requires a noun form to describe the brain.
• abundant: This means existing in large quantities, which does not apply to the context of brain development.

Correct answer: development

Explanation: The word 'development' fits well as it refers to the process of growth and change, which is appropriate in the context of the teenage brain's changes. It aligns grammatically and contextually with the idea of brain maturation.

Meaning: 'Development' refers to the process of growth or progress, particularly in the context of brain changes during adolescence.

Wrong options:

• enrichment: This implies improvement or enhancement, which does not capture the essence of the changes occurring in the teenage brain.
• adorning: This means decorating or adding beauty, which is irrelevant to the scientific context of brain changes.
• adoration: This refers to deep love or respect, which does not relate to the developmental processes of the brain.

Correct answer: both

Explanation: The word 'both' is appropriate as it indicates two elements being present, which fits the context of the sentence discussing fast-growing synapses and unconnected sections. It is grammatically correct and logically consistent.

Meaning: 'Both' means two items or elements together, emphasizing that young brains have two distinct characteristics.

Wrong options:

• few: This indicates a small number, which does not accurately describe the presence of two distinct features in the brain.
• whole: This means complete or entire, which does not fit the context of discussing specific characteristics of the brain.
• either: This implies a choice between two options, which does not apply to the context of having both features present.

Correct answer: impact

Explanation: The word 'impact' fits grammatically and contextually as it refers to the effect or influence of hormones on behavior. It aligns with the overall theme of external influences on teenage behavior.

Meaning: 'Impact' refers to the strong effect or influence that something has, particularly in the context of hormones affecting behavior.

Wrong options:

• impress: This means to make someone admire or respect, which does not fit the context of behavioral influence.
• impair: This means to weaken or damage, which does not accurately describe the influence of hormones in this context.
• impose: This means to force something upon someone, which does not relate to the effects of hormones on behavior.