Meaning: 'Controlled' means that the grid is managed or regulated by computers, indicating that the operation is automated and efficient.

Wrong options:

• has controlled: This form suggests a present perfect tense, which does not fit the context of describing a current state of management.
• hace controlled: This is a misspelling of 'has controlled' and is not a valid English phrase.
• had controlled: This past perfect tense implies an action completed before another past action, which is not relevant in this context.

Correct answer: in

Explanation: The preposition 'in' is appropriate here as it indicates the context or condition of existence. It fits grammatically and contextually, suggesting that the smart grid is more complex than anything that is currently present.

Meaning: 'In' refers to being within a certain state or condition, indicating that the smart grid surpasses the complexity of existing systems.

Wrong options:

• with: This preposition does not convey the intended meaning of comparison and would imply inclusion rather than a state of existence.
• without: This suggests absence, which contradicts the intended meaning of comparing complexity.
• of: This preposition does not correctly indicate the relationship between the smart grid and the existing systems.

Correct answer: slots

Explanation: The word 'slots' fits contextually as it refers to specific times or periods when consumers can choose to use electricity. It aligns with the idea of selecting the cheapest time for electricity usage, making it grammatically and contextually appropriate.

Meaning: 'Slots' refers to designated time periods or intervals, particularly in scheduling or planning contexts.

Wrong options:

• cuts: This term implies reductions or interruptions, which does not fit the context of time selection.
• pins: This word does not relate to time and suggests a physical attachment rather than a scheduling concept.
• points: While 'points' can refer to specific times, it does not convey the idea of intervals as effectively as 'slots' does.

Correct answer: do not exist

Explanation: The phrase 'do not exist' is grammatically correct in the present tense, indicating the current state of smart grids. It fits logically as it states that these grids are not available in reality, aligning with the overall context of the passage.

Meaning: 'Do not exist' means that smart grids are currently not present or available in the real world.

Wrong options:

• exist: This is a simple present tense that does not convey the negation needed in this context.
• does not exist: This form is incorrect because it does not agree with the plural subject 'grids.'
• existed: This past tense implies that smart grids were present in the past, which contradicts the current context.

Correct answer: into

Explanation: The preposition 'into' is appropriate here as it indicates the action of incorporating equipment failures within the grid for testing purposes. It fits grammatically and contextually, suggesting integration into the system.

Meaning: 'Into' indicates movement or inclusion within a space or system, in this case, referring to the failures being integrated into the grid for testing.

Wrong options:

• of: This preposition does not convey the intended meaning of incorporation and suggests possession rather than inclusion.
• onto: This implies a surface contact rather than integration, which does not fit the context of testing within the grid.
• above: This suggests a position over something rather than inclusion, making it contextually inappropriate.