In this sentence improvement item, decide whether the bracketed word "(than)" in the sentence about drawing on more natural experiments than just comparisons among continents needs any change.

Introduction / Context:
This question examines your ability to recognise correct comparative structures. The sentence talks about a student of human history drawing on many more natural experiments than just comparisons among the five inhabited continents. The bracketed word "than" links the comparison between "natural experiments" and "comparisons among continents". You must decide whether this word is already correct or should be replaced.

Given Data / Assumptions:

• Phrase: "many more natural experiments than just comparisons among the five inhabited continents".
• The comparison is between two types of evidence: natural experiments and simple comparisons.
• Bracketed word: "than".
• Options: "to", "of", "for", and "no improvement".

Concept / Approach:
In English, "more" as a comparative normally pairs with "than" to connect two elements. Examples include "more books than magazines" and "more evidence than speculation". In the given sentence, "many more natural experiments than just comparisons" is an entirely correct comparative structure. Changing "than" to "to", "of", or "for" would break this structure and make the sentence ungrammatical or unnatural.

Step-by-Step Solution:
Step 1: Identify the comparative word "more" in the phrase "many more natural experiments". Step 2: Note that the sentence is comparing natural experiments with "just comparisons among the five inhabited continents". Step 3: Recall that comparative adjectives and adverbs usually take "than" to introduce the second element of comparison. Step 4: Confirm that "than just comparisons" is the correct form. Step 5: Choose "no improvement" because the original usage is already correct.

Verification / Alternative check:
Test each alternative in the sentence. "More natural experiments to just comparisons" sounds incorrect and confuses the relationship between the elements. "More natural experiments of just comparisons" and "more natural experiments for just comparisons" are also wrong, because they replace a comparative connector with prepositions that change the meaning. Only "more natural experiments than just comparisons" keeps the standard comparative link between two types of evidence.

Why Other Options Are Wrong:
"To" might be used after "prefer" or "superior", but it does not function as the comparative connector for "more".

"Of" is used for possession or classification, as in "one of the continents", not for connecting comparative items after "more".

"For" indicates purpose or benefit, which does not match the structure of a direct comparison here.

Common Pitfalls:
Sometimes learners overthink simple comparative patterns and attempt to change prepositions that are already correct. A useful rule is to leave "more ... than ..." alone unless there is a very clear error elsewhere. When you see "more" or "less" followed by a second element of comparison, "than" is normally the correct and necessary connector. Recognising these fixed patterns allows you to confidently select "no improvement" when appropriate.

Final Answer:
The word "than" is correctly used in the comparative structure, so the best answer is "no improvement".