Meaning: 'Lifeblood' signifies something vital or indispensable for life or operation.

Wrong options:

• presence: Presence is a noun that refers to the state of being present, which does not convey the essential nature of mineral resources in this context.
• similar: Similar is an adjective that indicates likeness, which does not fit as it does not describe the role of mineral resources.
• endangers: Endangers is a verb that implies causing harm, which does not fit grammatically as it does not serve as a noun in this context.
• equivalent: Equivalent is an adjective that denotes equality in value, which does not fit as it does not describe the essential nature of mineral resources.
• impedes: Impedes is a verb meaning to hinder or obstruct, which does not fit grammatically as it does not serve as a noun in this context.

Correct answer: present

Explanation: The word 'present' functions as a noun here, indicating the current time or state, which is appropriate in the context of discussing the current status of mineral resources. It fits grammatically as it serves as the subject of the clause.

Meaning: 'Present' refers to the current time or moment.

Wrong options:

• lifeblood: Lifeblood is a noun that refers to something essential, which does not fit as it does not indicate time.
• similar: Similar is an adjective that does not denote a time frame and is not appropriate in this context.
• endangers: Endangers is a verb that does not fit grammatically as it does not indicate time.
• equivalent: Equivalent is an adjective that does not denote a time frame and is not appropriate in this context.
• impedes: Impedes is a verb that does not fit grammatically as it does not indicate time.

Correct answer: equivalent

Explanation: The term 'equivalent' is used as an adjective to indicate that coal, oil, and natural gas have a comparable value to 120 trillion tons of standard coal. This fits grammatically and contextually as it describes the relationship between the resources and their value.

Meaning: 'Equivalent' means equal in value, function, or meaning.

Wrong options:

• lifeblood: Lifeblood is a noun that does not fit as it does not describe a comparative value.
• endangers: Endangers is a verb that does not fit grammatically as it does not describe a comparative value.
• similar: Similar is an adjective that indicates likeness but does not convey the idea of equality in value.
• present: Present is a noun that refers to the current time and does not fit in the context of comparing values.
• impedes: Impedes is a verb that does not fit grammatically as it does not describe a comparative value.

Correct answer: endangers

Explanation: The verb 'endangers' indicates that acid mine drainage poses a risk to the health of plants, animals, and humans. This fits grammatically as it serves as the main verb of the clause, maintaining the logical flow of the sentence.

Meaning: 'Endangers' means to put at risk or in danger.

Wrong options:

• lifeblood: Lifeblood is a noun that does not fit as it does not convey an action or risk.
• presence: Presence is a noun that does not fit as it does not convey an action or risk.
• similar: Similar is an adjective that does not fit as it does not convey an action or risk.
• equivalent: Equivalent is an adjective that does not fit as it does not convey an action or risk.
• impedes: Impedes is a verb that means to hinder, which does not convey the same level of risk as 'endangers'.