Meaning: 'Evidence' refers to the available body of facts or information indicating whether a belief or proposition is true or valid.

Wrong options:

• likelihood: 'Likelihood' is a noun that refers to the chance of something happening, which does not fit as it does not indicate proof.
• marker: 'Marker' is a noun that typically refers to an object used to mark something, which is irrelevant in this context.
• unstable: 'Unstable' is an adjective describing something that is not stable, which does not fit as it does not serve as a noun in this sentence.
• wrapped: 'Wrapped' is a past participle that describes something covered or enclosed, which does not fit grammatically.
• frozen: 'Frozen' is a past participle that describes something that has been turned into ice, which does not fit as it does not indicate proof.
• exchanging: 'Exchanging' is a gerund that refers to the act of giving something and receiving something in return, which does not fit in this context.

Correct answer: frozen

Explanation: The term 'frozen' is a past participle that describes the state of the River Thames during the 17th century. It fits grammatically as it follows the verb 'was' and aligns with the context of discussing the river's condition.

Meaning: 'Frozen' means turned into ice or made very cold.

Wrong options:

• likelihood: 'Likelihood' is a noun that refers to the chance of something happening, which does not fit as it does not describe a state.
• marker: 'Marker' is a noun that does not relate to the condition of the river and is irrelevant here.
• evidence: 'Evidence' is a noun that indicates proof, which does not fit as it does not describe a state of the river.
• unstable: 'Unstable' is an adjective that describes something that is not stable, which does not fit as it does not describe the river's condition.
• wrapped: 'Wrapped' is a past participle that describes something covered, which does not fit in this context.
• exchanging: 'Exchanging' is a gerund that refers to the act of giving and receiving, which does not fit grammatically.

Correct answer: unstable

Explanation: The word 'unstable' is an adjective that describes the processes in the Sun as lacking stability. It fits grammatically as it follows the verb 'are' and aligns with the context of discussing the nature of solar processes.

Meaning: 'Unstable' means not stable; likely to change or fail.

Wrong options:

• likelihood: 'Likelihood' is a noun that refers to the chance of something happening, which does not fit as it does not describe a quality.
• marker: 'Marker' is a noun that does not relate to the processes in the Sun and is irrelevant here.
• evidence: 'Evidence' is a noun that indicates proof, which does not fit as it does not describe the processes.
• frozen: 'Frozen' is a past participle that describes something turned into ice, which does not fit in this context.
• wrapped: 'Wrapped' is a past participle that describes something covered, which does not fit grammatically.
• exchanging: 'Exchanging' is a gerund that refers to the act of giving and receiving, which does not fit in this context.

Correct answer: likelihood

Explanation: The term 'likelihood' is a noun that indicates the probability of an event occurring. It fits grammatically as it follows the verb 'is' and aligns with the context of discussing potential changes in temperature.

Meaning: 'Likelihood' refers to the chance or probability of something happening.

Wrong options:

• frozen: 'Frozen' is a past participle that describes a state, which does not fit as it does not indicate probability.
• evidence: 'Evidence' is a noun that indicates proof, which does not fit as it does not describe a probability.
• unstable: 'Unstable' is an adjective that describes something lacking stability, which does not fit as it does not indicate a chance.
• wrapped: 'Wrapped' is a past participle that describes something covered, which does not fit in this context.
• marker: 'Marker' is a noun that does not relate to probability and is irrelevant here.
• exchanging: 'Exchanging' is a gerund that refers to the act of giving and receiving, which does not fit grammatically.

Correct answer: steadily

Explanation: The word 'steadily' is an adverb that describes the manner in which the temperature is expected to increase. It fits grammatically as it modifies the verb 'get' and aligns with the context of discussing a gradual change.

Meaning: 'Steadily' means in a regular and even manner.

Wrong options:

• likelihood: 'Likelihood' is a noun that refers to the chance of something happening, which does not fit as it does not describe how the temperature changes.
• frozen: 'Frozen' is a past participle that describes a state, which does not fit in this context.
• evidence: 'Evidence' is a noun that indicates proof, which does not fit as it does not describe a manner of change.
• unstable: 'Unstable' is an adjective that describes something lacking stability, which does not fit as it does not describe the manner of change.
• wrapped: 'Wrapped' is a past participle that describes something covered, which does not fit grammatically.
• marker: 'Marker' is a noun that does not relate to the manner of temperature change and is irrelevant here.
• exchanging: 'Exchanging' is a gerund that refers to the act of giving and receiving, which does not fit in this context.