Meaning: 'Mustn't' means that it is necessary not to do something, in this case, not to hang around.

Wrong options:

• cannot: 'Cannot' indicates an inability to do something, which does not fit the context of a warning about behavior.
• could: 'Could' suggests a possibility or ability, which does not convey the urgency of avoiding danger.
• particularly: 'Particularly' is an adverb that emphasizes a specific aspect, but it does not fit grammatically as a verb in this context.
• couldn't: 'Couldn't' is the past tense of 'cannot,' which does not apply here as the sentence is in the present tense.
• all: 'All' is a determiner that does not fit grammatically as it does not convey a prohibition.
• have to: 'Have to' indicates necessity but lacks the prohibitive force needed in this context.
• should: 'Should' implies a recommendation rather than a strict prohibition, which is not strong enough for this warning.

Correct answer: cannot

Explanation: 'Cannot' indicates an inability to do something, which fits the context as it emphasizes that without the sense of smell, one is unable to identify many tastes.

Meaning: 'Cannot' means that it is impossible to do something, in this case, identify tastes without smell.

Wrong options:

• mustn't: 'Mustn't' indicates prohibition, which does not fit the context of inability to identify tastes.
• could: 'Could' suggests a past ability, which does not apply here as the statement is about present capabilities.
• particularly: 'Particularly' is an adverb that does not fit grammatically as it does not convey inability.
• couldn't: 'Couldn't' is the past tense of 'cannot,' which does not fit the present context of the sentence.
• all: 'All' is a determiner that does not fit grammatically as it does not convey inability.
• have to: 'Have to' indicates necessity but does not express the inability to identify tastes.
• should: 'Should' implies a recommendation rather than an inability, which is not appropriate here.

Correct answer: couldn't

Explanation: 'Couldn't' is the past tense of 'cannot,' indicating that participants were unable to identify the chocolate flavor during the experiment. This fits grammatically and contextually as it describes a specific outcome of the experiment.

Meaning: 'Couldn't' means that they were not able to do something in the past, in this case, identify the chocolate flavor.

Wrong options:

• mustn't: 'Mustn't' indicates prohibition, which does not fit the context of inability to identify flavors.
• cannot: 'Cannot' is present tense and does not fit the past context of the experiment.
• particularly: 'Particularly' is an adverb that does not fit grammatically as it does not convey inability.
• could: 'Could' suggests a past ability, which contradicts the context of not being able to identify the flavor.
• all: 'All' is a determiner that does not fit grammatically as it does not convey inability.
• have to: 'Have to' indicates necessity but does not express the inability to identify flavors.
• should: 'Should' implies a recommendation rather than an inability, which is not appropriate here.

Correct answer: have to

Explanation: 'Have to' indicates necessity, which fits the context as it emphasizes that sensing flavors is essential through smell rather than taste. This aligns with the overall message of the passage.

Meaning: 'Have to' means that it is necessary to do something, in this case, sense flavors through smell.

Wrong options:

• mustn't: 'Mustn't' indicates prohibition, which does not fit the context of necessity.
• cannot: 'Cannot' indicates inability, which does not apply to the necessity of sensing flavors.
• could: 'Could' suggests a past ability, which does not fit the context of necessity.
• particularly: 'Particularly' is an adverb that does not fit grammatically as it does not convey necessity.
• all: 'All' is a determiner that does not fit grammatically as it does not convey necessity.
• should: 'Should' implies a recommendation rather than a necessity, which is not strong enough for this context.
• couldn't: 'Couldn't' is the past tense of 'cannot,' which does not fit the present context of necessity.

Correct answer: could

Explanation: 'Could' indicates a past ability, which fits the context as it describes participants' capability to associate smells with memories from the past. This aligns with the overall message of the passage regarding memory and smell.

Meaning: 'Could' means that they were able to do something in the past, in this case, associate smells with memories.

Wrong options:

• mustn't: 'Mustn't' indicates prohibition, which does not fit the context of ability.
• cannot: 'Cannot' indicates inability, which contradicts the context of being able to associate smells with memories.
• particularly: 'Particularly' is an adverb that does not fit grammatically as it does not convey ability.
• couldn't: 'Couldn't' is the past tense of 'cannot,' which contradicts the context of being able to associate smells.
• all: 'All' is a determiner that does not fit grammatically as it does not convey ability.
• have to: 'Have to' indicates necessity but does not express the ability to associate smells.
• should: 'Should' implies a recommendation rather than an ability, which is not appropriate here.