Researchers studying ancient urbanization have determined that the city of Teotihuacan housed over 125,000 residents at its peak around 450...

Sentence Structure

• Researchers studying ancient urbanization
  • have determined
    • that the city of Teotihuacan
      • housed over 125,000 residents
        • at its peak around 450 CE

• [?]

• was unprecedented for any city in the pre-Columbian Americas

Understanding the Meaning

Let's start from the beginning:

'Researchers studying ancient urbanization have determined that the city of Teotihuacan housed over 125,000 residents at its peak around 450 CE'

This tells us:

• Researchers studying old cities found something specific
  • The city of Teotihuacan had over 125,000 people living in it
  • This was around 450 CE (Common Era)

This is where we have the blank.

Let's look at the choices:

• A: CE. This
• B: CE, this
• C: CE this
• D: CE; making this

To see what works here, let's read the rest of the sentence and understand what it's saying!

The sentence continues: 'was unprecedented for any city in the pre-Columbian Americas.'

This means:

• No other city in the Americas (before Columbus arrived) had ever had such a large population before
• This population size was a first - something that had never happened before

Now, what do we notice about the structure here?

Let's look at what comes before the blank:

• 'Researchers studying ancient urbanization have determined that the city of Teotihuacan housed over 125,000 residents at its peak around 450 CE'
  • This is a complete thought that could stand on its own
  • It has a subject (Researchers), a verb (have determined), and expresses a complete idea

And what comes after the blank:

• 'This was unprecedented for any city in the pre-Columbian Americas'
  • This is also a complete thought that could stand on its own
  • It has a subject (This), a verb (was), and expresses a complete idea

So we have two complete sentences!

When you have two complete sentences, you need to either:

• Separate them with a period (and start the second one with a capital letter)
• OR connect them properly with a semicolon or comma + connecting word

You cannot just use a comma by itself or run them together with no punctuation.

The correct answer is Choice A: CE. This

This properly separates the two complete sentences with a period and starts the new sentence with a capital letter.

GRAMMAR CONCEPT APPLIED

Separating Two Complete Sentences

When you have two complete sentences (each with its own subject and verb, expressing complete thoughts), you must separate or connect them properly:

Option 1: Period + Capital Letter

• First complete sentence: "The experiment yielded surprising results."
• Second complete sentence: "This discovery changed the field."
• Notice how each could stand alone

Option 2: Semicolon (when closely related)

• "The experiment yielded surprising results; this discovery changed the field."
• Both sentences are closely connected in meaning

What NOT to do:

Comma alone (comma splice):

• WRONG: "The experiment yielded surprising results, this discovery changed the field."

No punctuation (run-on):

• WRONG: "The experiment yielded surprising results this discovery changed the field."

In our question:

• First complete sentence: "Researchers...determined that the city...housed over 125,000 residents at its peak around 450 CE"
• Second complete sentence: "This was unprecedented for any city in the pre-Columbian Americas"
• These needed to be separated with a period, making Choice A correct