Meaning: 'At the same time' means occurring simultaneously or concurrently.

Wrong options:

• respectively: Respectively is used to indicate that two or more items correspond to each other in the order mentioned, which does not fit the context of simultaneous actions here.
• adult: Adult refers to a fully grown person and does not relate to the simultaneous nature of the actions described.
• explored: Explored is a past tense verb that does not fit grammatically in this context, as the blank requires a phrase indicating simultaneous actions.
• exploring: Exploring is a present participle that does not fit the context of the sentence, which is focused on contrasting behaviors.

Correct answer: exploring

Explanation: The word 'exploring' is a present participle that indicates an ongoing action. It fits grammatically as it describes what the physicians are currently doing in relation to the adolescent brain.

Meaning: Exploring means to investigate or examine something in detail.

Wrong options:

• explored: Explored is the past tense of explore, which does not fit the context of ongoing research being conducted by the physicians.
• adult: Adult does not relate to the action of investigating and is irrelevant in this context.
• respectively: Respectively does not fit as it does not convey any action related to research or investigation.
• unique: Unique is an adjective and does not serve as a verb, making it unsuitable for this blank.

Correct answer: unique

Explanation: The word 'unique' is an adjective that describes the distinct characteristics of the adolescent brain. It fits grammatically and contextually as it emphasizes the special nature of the brain being studied.

Meaning: Unique means being the only one of its kind; unlike anything else.

Wrong options:

• exploring: Exploring is a verb and does not fit as an adjective to describe the structure of the brain.
• adolescent: Adolescent is an adjective that describes a person in their teenage years, but it does not describe the structure itself.
• adult: Adult is an adjective that refers to a fully grown person and does not apply to the context of describing the brain's structure.
• respectively: Respectively does not fit as it does not describe a quality or characteristic.

Correct answer: adolescent

Explanation: The word 'adolescent' is an adjective that specifically refers to the developmental stage of teenagers. It fits grammatically and contextually as it describes the type of brain being studied.

Meaning: Adolescent refers to a young person in the stage of development between childhood and adulthood.

Wrong options:

• exploring: Exploring is a verb and does not fit as a descriptor for the brain.
• unique: Unique is an adjective that describes something distinct but does not specify the age group of the brain in question.
• adult: Adult refers to a fully grown person and does not apply to the context of the teenage brain.
• respectively: Respectively does not fit as it does not describe a quality or characteristic.

Correct answer: development

Explanation: The word 'development' is a noun that refers to the process of growth or progress. It fits grammatically and contextually as it describes the ongoing changes occurring in the teenage brain.

Meaning: Development refers to the process of developing or being developed, particularly in terms of growth and maturation.

Wrong options:

• exploring: Exploring is a verb and does not fit as a noun to describe the process of change.
• adult: Adult refers to a fully grown person and does not relate to the process of growth in this context.
• unique: Unique is an adjective and does not serve as a noun to describe a process.
• respectively: Respectively does not fit as it does not describe a process or state of change.