Meaning: Toxins are harmful substances that can cause damage to living organisms.

Wrong options:

• microbes: 'Microbes' refers to microscopic organisms, which do not fit the context of poisonous substances carried by amphibians.
• partners: 'Partners' is a noun that implies a relationship or collaboration, which is irrelevant in the context of poisonous substances.
• intensified: 'Intensified' is a verb form that does not fit grammatically or contextually as it does not describe a substance carried by amphibians.
• tissues: 'Tissues' is a plural noun referring to groups of cells, which does not fit as it does not describe a substance but rather a part of the organism.

Correct answer: tissues

Explanation: The term 'tissues' is a plural noun that refers to groups of cells in an organism. It fits grammatically as it aligns with the plural subject 'amphibians' and contextually as it describes where toxins can be found within these animals.

Meaning: Tissues are collections of cells that perform specific functions in an organism.

Wrong options:

• secreted: 'Secreted' is a verb that does not fit as it does not describe a physical part of the amphibians.
• partners: 'Partners' is a noun that does not relate to the biological context of amphibians' anatomy.
• toxins: 'Toxins' is already used in the first blank and does not fit here as it does not refer to a part of the organism.
• intensified: 'Intensified' is a verb that does not fit grammatically or contextually as it does not describe a part of the organism.

Correct answer: secreted

Explanation: The word 'secreted' is the past participle of the verb 'to secrete,' meaning to produce and release a substance. It fits grammatically as it describes the action performed by the poison dart frogs and contextually as it relates to how the toxins are produced.

Meaning: Secreted means to produce and release a substance, often used in biological contexts.

Wrong options:

• microbes: 'Microbes' refers to microscopic organisms and does not fit as it does not describe an action related to toxins.
• partners: 'Partners' is a noun that does not relate to the action of producing toxins.
• toxins: 'Toxins' is a noun and does not fit as it does not describe an action but rather the substances themselves.
• intensified: 'Intensified' is a verb that does not fit grammatically or contextually as it does not describe the action of producing toxins.

Correct answer: deadly

Explanation: The word 'deadly' is an adjective that describes something capable of causing death. It fits grammatically as it modifies the noun 'chemicals' and contextually as it describes the effect of the toxins on humans.

Meaning: Deadly means capable of causing death or extremely harmful.

Wrong options:

• secreted: 'Secreted' is a verb that does not fit as it does not describe the nature of the chemicals.
• microbes: 'Microbes' refers to microscopic organisms and does not fit as it does not describe the effect of the chemicals.
• partners: 'Partners' is a noun that does not relate to the harmful nature of the chemicals.
• intensified: 'Intensified' is a verb that does not fit grammatically or contextually as it does not describe the nature of the chemicals.