Meaning: 'Claim' means a statement that something is true, often without proof, which in this case refers to Wegener's assertion about continental drift.

Wrong options:

• ability: 'Ability' refers to the capacity to do something, which does not fit the context of a scientific assertion.
• concern: 'Concern' implies worry or interest, which does not accurately describe Wegener's declaration about the continents.
• invention: 'Invention' suggests the creation of something new, which does not apply to Wegener's assertion about existing continents.

Correct answer: seriously

Explanation: The adverb 'seriously' fits grammatically and contextually, indicating that no one took Wegener's ideas with the gravity they deserved. It conveys the sentiment that his work was dismissed rather than considered thoughtfully.

Meaning: 'Seriously' means in a serious manner, indicating that people did not regard his ideas as important or worthy of consideration.

Wrong options:

• fairly: 'Fairly' suggests a moderate degree, which does not convey the dismissive attitude towards Wegener's work.
• sensibly: 'Sensibly' implies a rational approach, which does not match the context of dismissal; it suggests that people should have taken it into account.
• regrettably: 'Regrettably' implies a sense of sorrow about the situation, which does not fit the context of how his work was received.

Correct answer: by

Explanation: The preposition 'by' fits grammatically and contextually, indicating the agent or means through which the realization occurred. It connects the time frame of the early 1960s with the actions of geologists.

Meaning: 'By' indicates the means or agent through which something happens, in this case, the realization of geologists.

Wrong options:

• over: 'Over' suggests a duration or a covering, which does not fit the context of the realization occurring at a specific time.
• from: 'From' indicates a starting point, which does not convey the correct relationship between the time and the realization.
• to: 'To' suggests direction or purpose, which does not accurately describe the relationship in this context.

Correct answer: were beginning

Explanation: The phrase 'were beginning' fits grammatically as the past continuous tense, indicating an action that was ongoing in the past. It aligns contextually with the timeline of the early 1960s when geologists started to realize something significant about continental drift.

Meaning: 'Were beginning' indicates that the action of realizing was in progress during that time period.

Wrong options:

• are beginning: 'Are beginning' is present tense, which does not match the past context of the sentence.
• have begun: 'Have begun' suggests a completed action in the present perfect tense, which does not fit the ongoing realization described.
• begin: 'Begin' is in the base form and does not fit grammatically in this past context.

Correct answer: each other

Explanation: The phrase 'each other' fits grammatically and contextually, indicating a reciprocal relationship between the continents as they drift apart. It emphasizes the interaction between the continents in the geological process described.

Meaning: 'Each other' refers to a mutual relationship, indicating that the continents are moving away from one another.

Wrong options:

• another: 'Another' implies one additional item, which does not fit the context of multiple continents moving apart.
• any other: 'Any other' suggests a non-specific alternative, which does not convey the reciprocal relationship needed here.
• the other: 'The other' implies a specific counterpart, which does not accurately describe the relationship among multiple continents.