Meaning: In this context, 'rock' refers to extremely low prices, often used in phrases like 'rock bottom' to indicate the lowest possible level.

Wrong options:

• cheap: While 'cheap' suggests low cost, it does not fit the idiomatic expression 'rock bottom prices' which conveys a more severe connotation.
• very: The word 'very' is an adverb and does not appropriately describe prices in this context, as it lacks a noun to modify.
• stone: Similar to 'rock', 'stone' could imply low prices, but it is not commonly used in the idiomatic expression 'rock bottom', making it less fitting.

Correct answer: their

Explanation: The word 'their' correctly indicates possession, referring to the crops belonging to the growers. It fits grammatically and contextually, as it aligns with the subject of the sentence, which is the growers.

Meaning: 'Their' is a possessive pronoun used to indicate that something belongs to them, in this case, the crops that the growers own.

Wrong options:

• then: 'Then' is an adverb indicating time and does not fit grammatically or contextually as it does not indicate possession.
• the: 'The' is a definite article and does not convey possession, making it unsuitable in this context.
• some: 'Some' is an indefinite pronoun that does not indicate ownership, thus failing to fit the grammatical structure of the sentence.

Correct answer: development

Explanation: The word 'development' fits grammatically as a noun that describes the process of creating new insecticides. It aligns contextually with the positive advancements in pest control mentioned in the passage.

Meaning: 'Development' refers to the process of growth or advancement, particularly in creating new products or technologies, in this case, insecticides.

Wrong options:

• freedom: 'Freedom' does not relate to the context of pest control and does not fit grammatically as it does not describe a process relevant to insecticides.
• research: While 'research' could relate to the study of insecticides, it does not convey the idea of creating or producing new products, making it less suitable here.
• discharge: 'Discharge' refers to the act of releasing something and does not fit the context of advancements in pest control.

Correct answer: entire

Explanation: The word 'entire' fits grammatically as it describes the whole scope of history, emphasizing completeness. It aligns contextually with the statement about the best tools available in pest control.

Meaning: 'Entire' means whole or complete, indicating that the tools available are the best throughout the full history of synthetic chemicals.

Wrong options:

• full: 'Full' could imply completeness but is less commonly used in this context compared to 'entire', which is more precise in describing history.
• complete: 'Complete' is an adjective that could fit, but 'entire' is more idiomatic in this context, making it the preferred choice.
• perfect: 'Perfect' implies flawlessness, which does not fit the context of describing the history of synthetic chemicals, as it does not convey the same meaning as 'entire'.

Correct answer: large

Explanation: The word 'large' fits grammatically as it describes the scale of using new chemistry. It aligns contextually with the idea of significant or extensive application of the new insecticides.

Meaning: 'Large' refers to a considerable size or extent, indicating that the farmers have not used the new chemistry on a significant scale.

Wrong options:

• great: 'Great' can imply a large amount but is more subjective and less precise than 'large' in this context.
• long: 'Long' typically refers to duration or distance, which does not fit the context of scale in this sentence.
• total: 'Total' implies completeness but does not convey the same sense of size or extent as 'large', making it less appropriate.