Meaning: In this context, 'level' refers to the degree or amount of carbon prices that have increased.

Wrong options:

• credit: The term 'credit' refers to a financial concept or acknowledgment, which does not relate to the measurement of carbon prices in this context.
• sources: While 'sources' refers to origins or providers, it does not fit as it does not describe a measurement or extent of carbon prices.
• target: Although 'target' can refer to a goal, it does not appropriately describe the current state of carbon prices as a measurable extent.
• because: 'Because' is a conjunction used to introduce a reason, which does not fit as a noun to describe the highest point of carbon prices.
• unless: 'Unless' is a conjunction that introduces a condition, which does not fit in the context of describing carbon prices.
• link: The term 'link' refers to a connection or relationship, which does not describe a measurement of carbon prices.

Correct answer: because

Explanation: The word 'because' serves as a conjunction that introduces the reason for the rise in carbon prices, making it grammatically and contextually appropriate in this sentence.

Meaning: 'Because' is used to indicate the reason or cause for something, in this case, the rise in carbon prices due to changes in the emissions trading system.

Wrong options:

• level: 'Level' is a noun that does not function as a conjunction and cannot introduce a reason in this context.
• sources: 'Sources' is a noun that refers to origins or providers, which does not fit as a conjunction to explain the reason for the price increase.
• target: 'Target' is a noun that refers to a goal, which does not serve the purpose of introducing a reason in this sentence.
• unless: 'Unless' is a conjunction that introduces a condition, which does not fit as it does not provide a reason for the rise in carbon prices.
• link: 'Link' is a noun that refers to a connection, which does not serve as a conjunction to explain the cause of the price increase.
• credit: 'Credit' is a noun that does not function as a conjunction and cannot introduce a reason.

Correct answer: target

Explanation: The term 'target' is a noun that refers to a goal or objective, which fits grammatically and contextually as it describes the EU's aim of becoming carbon-neutral by 2050.

Meaning: In this context, 'target' refers to a specific goal set by the EU regarding carbon neutrality.

Wrong options:

• level: 'Level' refers to a degree or extent, which does not appropriately describe a goal or objective in this context.
• sources: 'Sources' refers to origins or providers, which does not fit as it does not describe a goal related to carbon neutrality.
• because: 'Because' is a conjunction that introduces a reason, which does not fit as a noun to describe a goal.
• unless: 'Unless' is a conjunction that introduces a condition, which does not fit as it does not describe a goal or target.
• link: 'Link' is a noun that refers to a connection, which does not describe a goal or target in this context.
• credit: 'Credit' is a noun that does not relate to the concept of a goal or target.

Correct answer: sources

Explanation: The word 'sources' is a plural noun that refers to the origins or providers of cleaner energy, fitting grammatically and contextually as it describes the types of energy businesses are encouraged to switch to.

Meaning: In this context, 'sources' refers to the different types of cleaner energy that businesses can utilize.

Wrong options:

• level: 'Level' refers to a degree or extent, which does not fit as it does not describe types of energy.
• target: 'Target' refers to a goal, which does not fit as it does not describe types of energy sources.
• because: 'Because' is a conjunction that introduces a reason, which does not fit as a noun to describe energy types.
• unless: 'Unless' is a conjunction that introduces a condition, which does not fit as it does not describe energy sources.
• link: 'Link' is a noun that refers to a connection, which does not describe types of energy sources.
• credit: 'Credit' is a noun that does not relate to the concept of energy sources.