Meaning: 'But' is used to introduce a statement that contrasts with or seems to contradict something that has been said previously.

Wrong options:

• and: 'And' is a conjunction that adds information rather than contrasting it, making it unsuitable for this context.
• or: 'Or' suggests an alternative, which does not fit the contrasting nature of the sentence.
• almost: 'Almost' indicates proximity but does not provide the necessary contrast required in this sentence.

Correct answer: fastest

Explanation: The word 'fastest' is the superlative form of 'fast,' which is appropriate here as it describes the Black Mamba as one of the quickest snakes in comparison to all others. This aligns with the grammatical structure of the sentence, which requires a superlative to convey the highest degree of speed.

Meaning: 'Fastest' means the most quick or rapid, indicating that the Black Mamba is among the quickest snakes in the world.

Wrong options:

• fast: 'Fast' is the base form and does not convey the superlative degree needed in this context.
• most fast: 'Most fast' is grammatically incorrect as 'fastest' is the correct superlative form.
• more fast: 'More fast' is also incorrect; 'fastest' is the proper superlative form.

Correct answer: which

Explanation: The word 'which' is a relative pronoun that introduces a non-defining clause, providing additional information about the venom. It fits grammatically and contextually, as it connects the clause to the noun 'venom' and specifies which venom is being discussed.

Meaning: 'Which' is used to refer to a specific thing or group of things, in this case, the venom of the Black Mamba.

Wrong options:

• when: 'When' is a conjunction that refers to time, which does not fit the context of describing the venom.
• who: 'Who' is a pronoun used for people, not suitable for referring to venom, which is an inanimate object.
• that: 'That' could be used, but 'which' is more appropriate in this non-defining context.

Correct answer: cause

Explanation: The word 'cause' is a verb that indicates the action of producing an effect, which fits grammatically and contextually as it describes what the venom does to the victim's nervous system and heart. It is the correct choice to convey the intended meaning of the sentence.

Meaning: 'Cause' means to make something happen or to bring about an effect, in this case, damage to the nervous system and heart.

Wrong options:

• make: 'Make' is a more general term and does not specifically convey the idea of producing an effect as clearly as 'cause.'
• avoid: 'Avoid' implies preventing something from happening, which is the opposite of what the venom does.
• force: 'Force' suggests coercion or compulsion, which does not accurately describe the action of the venom.

Correct answer: rate

Explanation: The word 'rate' is a noun that refers to the frequency or level of occurrence, which fits grammatically and contextually as it describes the mortality statistic associated with the venom. It is the correct term to convey the concept of mortality in this context.

Meaning: 'Rate' refers to a measure, quantity, or frequency, particularly in relation to a specific event, such as mortality in this case.

Wrong options:

• rating: 'Rating' typically refers to an evaluation or assessment, which does not fit the context of mortality statistics.
• rated: 'Rated' is a past participle that does not function as a noun in this context, making it grammatically incorrect.
• rates: 'Rates' is the plural form of 'rate,' which does not fit the singular context of the mortality statistic being discussed.