Meaning: 'Infected' means that someone has been affected by a disease or bacteria, in this case, tuberculosis.

Wrong options:

• been infected: This option is incorrect because 'been infected' requires an auxiliary verb to form a complete tense, making it grammatically unsuitable in this context.
• who infected: This option is incorrect as it suggests an active role of the people in infecting others, which does not fit the intended meaning of the sentence.
• which is infected: This option is incorrect because 'which is infected' implies a specific subject that is not present in the sentence, making it grammatically and contextually inappropriate.

Correct answer: However

Explanation: The word 'However' serves as a discourse marker that introduces a contrast to the previous statement about most people not developing active TB. It fits logically and contextually to indicate that despite the previous information, there is an exception regarding people with weak body defense systems.

Meaning: 'However' means 'on the other hand' or 'nevertheless,' indicating a contrast or exception to what has been previously stated.

Wrong options:

• For this reason: This option is incorrect because it suggests a cause-and-effect relationship, which does not align with the contrasting information being presented.
• In fact: This option is incorrect as it implies a confirmation of the previous statement rather than introducing a contrast, which is the intended function here.
• Thus: This option is incorrect because it indicates a conclusion or result, which does not fit the context of contrasting the previous statement.

Correct answer: damage

Explanation: The word 'damage' is a verb that appropriately describes the harmful effect TB can have on a person's lungs or body. It fits grammatically as it is in the base form, suitable for the modal verb structure implied in the sentence.

Meaning: 'Damage' means to cause physical harm or injury to something, in this case, a person's lungs or body.

Wrong options:

• wound: This option is incorrect because 'wound' is primarily a noun and does not fit grammatically as a verb in this context.
• injure: This option is incorrect as 'injure' is a verb that implies causing harm, but it is less commonly used in this context compared to 'damage.'
• hurt: This option is incorrect because 'hurt' is more informal and does not convey the same level of severity as 'damage' in a medical context.

Correct answer: cause

Explanation: The word 'cause' is a verb that fits grammatically and contextually, indicating that TB can lead to serious sickness. It is in the base form, which is appropriate following the modal verb structure implied in the sentence.

Meaning: 'Cause' means to make something happen, in this case, serious sickness resulting from TB.

Wrong options:

• make: This option is incorrect because 'make' is too vague and does not specifically convey the idea of leading to a negative outcome like 'cause' does.
• do: This option is incorrect as 'do' does not fit the context of leading to an effect; it is more general and lacks the specificity required here.
• perform: This option is incorrect because 'perform' typically refers to carrying out an action or task, which does not align with the context of causing illness.

Correct answer: who

Explanation: The word 'who' is a relative pronoun that correctly refers to people, fitting grammatically and contextually as it introduces a clause that provides more information about the subject of the sentence.

Meaning: 'Who' is used to refer to people or individuals, in this case, those who have active TB.

Wrong options:

• whom: This option is incorrect because 'whom' is used as an object in a sentence, while 'who' is the subject here, making 'who' the correct choice.
• whose: This option is incorrect as 'whose' indicates possession, which does not fit the context of describing people with TB.
• which: This option is incorrect because 'which' is used for things or animals, not people, making it grammatically inappropriate in this context.