Meaning: 'Process' means a series of actions or steps taken to achieve a particular end, in this case, the act of breathing.

Wrong options:

• procedure: 'Procedure' implies a specific method or set of steps, which is too formal and does not capture the general nature of breathing as described here.
• routine: 'Routine' suggests a regular or habitual practice, which does not encompass the biological aspect of breathing as a natural function.
• custom: 'Custom' refers to a traditional practice or behavior, which is not applicable to the biological process of breathing.
• habit: 'Habit' indicates a regular practice or behavior, but it lacks the scientific connotation that 'process' provides in this context.

Correct answer: because

Explanation: The word 'because' introduces a reason, linking the need for air directly to its content of oxygen, which is essential for energy release. This fits both grammatically and contextually, as it provides a logical explanation for the preceding statement.

Meaning: 'Because' means for the reason that; it introduces a cause or explanation for needing air.

Wrong options:

• so: 'So' indicates a consequence rather than a reason, making it inappropriate for explaining why air is needed.
• when: 'When' introduces a time condition, which does not fit the causal relationship required in this context.
• till: 'Till' suggests a time limit or condition, which does not apply to the need for air.
• also: 'Also' adds additional information but does not provide the necessary causal link.

Correct answer: contained

Explanation: The word 'contained' is the past participle form that describes the energy as being held within the food. It fits grammatically as it follows the structure of the sentence, indicating the energy that is present in the food.

Meaning: 'Contained' means held within something; in this case, it refers to the energy that is held within food.

Wrong options:

• containing: 'Containing' is a present participle that does not fit the past tense structure of the sentence, which requires a past participle here.
• contains: 'Contains' is present tense and does not match the past context needed in this sentence.
• being contained: 'Being contained' is a gerund phrase that complicates the sentence unnecessarily and does not fit the grammatical structure required.

Correct answer: times

Explanation: The word 'times' fits grammatically as it refers to the frequency of breathing in and out, which is measured in occurrences per minute. It aligns with the context of the sentence, which discusses the number of breaths taken.

Meaning: 'Times' refers to the number of occurrences or repetitions of an action, in this case, the act of breathing.

Wrong options:

• periods: 'Periods' suggests intervals of time rather than the frequency of breaths, making it contextually inappropriate.
• items: 'Items' refers to distinct objects or things, which does not apply to the act of breathing.
• sessions: 'Sessions' implies a set period of activity, which does not accurately describe the continuous nature of breathing.
• breaths: 'Breaths' is a noun that could fit, but it does not match the grammatical requirement for a measure of frequency in this context.

Correct answer: so

Explanation: The word 'so' indicates a consequence or result, linking the need for more energy to the need for more oxygen. It fits grammatically and contextually, as it shows the relationship between the two clauses.

Meaning: 'So' means for that reason; it introduces a result or conclusion based on the previous statement.

Wrong options:

• in fact: 'In fact' is used to emphasize a statement but does not indicate a causal relationship, making it unsuitable here.
• finally: 'Finally' suggests a conclusion or last point, which does not fit the logical flow of the sentence.
• because: 'Because' indicates a reason, but it would create redundancy in this context since the reason has already been established.
• after: 'After' indicates a sequence in time, which does not apply to the causal relationship being expressed.