A.I. Explanation:

Correct answer: that

Explanation: The word 'that' serves as a conjunction introducing a clause that explains what Einstein stated. It fits grammatically as it connects the main clause to the subordinate clause, maintaining the flow of the sentence.

Meaning: 'That' is used to introduce a statement or explanation.

Wrong options:

• this: 'This' is a demonstrative pronoun that refers to something nearby or just mentioned, which does not fit as it does not introduce a clause.
• on: 'On' is a preposition that does not serve to introduce a clause and is grammatically incorrect in this context.
• into: 'Into' is a preposition indicating movement towards the inside of something, which does not fit the grammatical structure needed here.
• occurence: 'Occurence' is a noun and does not function as a conjunction, making it unsuitable for this blank.
• happened: 'Happened' is a verb in the past tense, which does not fit as it does not connect clauses.

Correct answer: occurence

Explanation: The term 'occurence' is a noun that refers to an event or incident. It fits grammatically as it serves as the subject of the clause, aligning with the context of discussing events in time.

Meaning: 'Occurence' means an event or something that happens.

Wrong options:

• another: 'Another' is a determiner that refers to an additional item, which does not fit as it does not describe an event.
• this: 'This' is a demonstrative pronoun that does not function as a noun and cannot serve as the subject here.
• that: 'That' is a demonstrative pronoun that does not fit as it does not refer to an event or incident.
• happened: 'Happened' is a verb that does not fit grammatically as it cannot serve as a noun in this context.
• on: 'On' is a preposition and does not serve as a noun, making it unsuitable.

Correct answer: another

Explanation: The word 'another' is a determiner that refers to an additional observer, fitting grammatically and contextually as it indicates a different person in the scenario being described.

Meaning: 'Another' means one more or an additional one.

Wrong options:

• this: 'This' is a demonstrative pronoun that refers to something nearby, which does not fit as it does not indicate an additional observer.
• that: 'That' is a demonstrative pronoun that refers to something previously mentioned, which does not fit in this context.
• occurence: 'Occurence' is a noun that does not fit as it does not refer to a person or observer.
• happened: 'Happened' is a verb that does not fit grammatically as it cannot serve as a determiner in this context.
• into: 'Into' is a preposition that does not refer to a person and is therefore unsuitable.

Correct answer: into

Explanation: The word 'into' is a preposition that indicates movement towards the inside of something, fitting grammatically as it describes the direction of looking back in time.

Meaning: 'Into' indicates movement towards the inside or interior of something.

Wrong options:

• this: 'This' is a demonstrative pronoun that does not indicate direction and is not suitable here.
• that: 'That' is a demonstrative pronoun that does not indicate movement and is therefore incorrect.
• on: 'On' is a preposition that indicates a position but does not convey the sense of movement required in this context.
• occurence: 'Occurence' is a noun and does not function as a preposition, making it unsuitable for this blank.
• happened: 'Happened' is a verb that does not fit grammatically as it cannot serve as a preposition.