Meaning: 'To' indicates direction or relationship, in this case, linking the name to the phenomenon.

Wrong options:

• from: The preposition 'from' indicates a source or origin, which does not fit the context of naming a phenomenon.
• which: The word 'which' is a relative pronoun and does not serve as a preposition, making it grammatically incorrect here.
• when: The word 'when' is an adverb that indicates time, which does not relate to the naming of a phenomenon.
• ever: The word 'ever' is an adverb that expresses time but does not fit as a preposition in this context.
• therefore: The word 'therefore' is a conjunctive adverb that indicates a conclusion, which does not fit the grammatical structure needed here.
• thus: The word 'thus' is also a conjunctive adverb indicating a result, which does not fit as a preposition.

Correct answer: which

Explanation: The word 'which' is a relative pronoun that introduces a clause providing more information about the phenomenon. It fits grammatically as it connects the clause to the noun 'phenomenon' appropriately.

Meaning: 'Which' is used to introduce a clause that gives additional information about something previously mentioned.

Wrong options:

• from: The word 'from' is a preposition indicating origin, which does not fit the context of introducing a clause.
• to: The word 'to' is a preposition that does not serve as a relative pronoun, making it incorrect here.
• when: The word 'when' is an adverb that indicates time, which does not relate to the clause structure needed here.
• ever: The word 'ever' is an adverb that does not function as a relative pronoun and is therefore incorrect in this context.
• therefore: The word 'therefore' is a conjunctive adverb that indicates a conclusion, which does not fit the grammatical structure needed here.
• thus: The word 'thus' is also a conjunctive adverb indicating a result, which does not fit as a relative pronoun.

Correct answer: ever

Explanation: The word 'ever' is an adverb that emphasizes the ongoing or continuous nature of the phenomenon being described. It fits grammatically as it modifies the adjective 'apparent' to indicate that it is always or at any time noticeable.

Meaning: 'Ever' means at any time or always, emphasizing the continuous nature of the phenomenon.

Wrong options:

• from: The word 'from' is a preposition that does not fit as an adverb modifying 'apparent.'
• which: The word 'which' is a relative pronoun and does not serve as an adverb, making it incorrect here.
• when: The word 'when' is an adverb that indicates time but does not fit the context of describing the apparent nature of something.
• to: The word 'to' is a preposition that does not function as an adverb in this context.
• therefore: The word 'therefore' is a conjunctive adverb that indicates a conclusion, which does not fit the grammatical structure needed here.
• thus: The word 'thus' is also a conjunctive adverb indicating a result, which does not fit as an adverb modifying 'apparent.'

Correct answer: thus

Explanation: The word 'thus' is a conjunctive adverb that indicates a result or consequence. It fits grammatically as it connects the preceding clause about high frequency words to the effect they have on the brain's encoding of information.

Meaning: 'Thus' means as a result or in this way, indicating a consequence of the previous statement.

Wrong options:

• from: The word 'from' is a preposition that does not fit as a conjunctive adverb indicating a result.
• which: The word 'which' is a relative pronoun and does not serve as a conjunctive adverb, making it incorrect here.
• when: The word 'when' is an adverb that indicates time, which does not relate to the causal relationship needed here.
• ever: The word 'ever' is an adverb that does not indicate a result and is therefore incorrect in this context.
• therefore: The word 'therefore' is a conjunctive adverb that indicates a conclusion, which is similar but does not fit the specific context of this sentence as well as 'thus.'