In 2018, astronomer Dr. Patricia Chen was analyzing spectral data from a distant star system when she detected unusual radio...

Sentence Structure

• In 2018,
  • astronomer Dr. Patricia Chen
    • was analyzing spectral data from a distant star system
      • when she detected unusual radio wave frequencies
        • in the observations [?]
• [with/. With/, with/so with] the application of signal filtering algorithms,
  • she determined
    • the frequencies originated from a rapidly rotating neutron star.

Understanding the Meaning

Let's start reading from the beginning:

In 2018, Dr. Patricia Chen (an astronomer) was doing something:

• She was analyzing spectral data from a distant star system
• While doing this analysis, she detected unusual radio wave frequencies
• These frequencies were in the observations

So far we have a complete thought: Dr. Chen detected these unusual frequencies in the observations.

This is where we have the blank. Let's look at the choices:

• A: observations with
• B: observations. With (a period, then capital W)
• C: observations, with (a comma)
• D: observations so with

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

After the blank, we have:
"the application of signal filtering algorithms, she determined the frequencies originated from a rapidly rotating neutron star."

Now let's understand what this is telling us:

• "With the application of signal filtering algorithms"
  • This tells us HOW she figured something out
  • She used these algorithms as a tool
• "she determined the frequencies originated from a rapidly rotating neutron star"
  • This is what she figured out
  • The frequencies came from a neutron star

So the second part means: By using signal filtering algorithms, she determined where the frequencies came from.

What do we notice about the structure here?

• The first part: "she detected unusual radio wave frequencies in the observations"
  • This is a complete thought - it could stand alone as a sentence
  • Subject = she, Verb = detected, Object = frequencies
• The second part: "she determined the frequencies originated from a rapidly rotating neutron star"
  • This is ALSO a complete thought - it could stand alone as a sentence
  • Subject = she, Verb = determined, Object = what she determined
  • Note: "With the application of signal filtering algorithms" is just extra information telling us HOW she determined this

We have two complete sentences here - two independent thoughts that each need to stand on their own.

The correct answer is B (observations. With)

This properly separates the two complete thoughts with a period, creating two sentences.

GRAMMAR CONCEPT APPLIED

Separating Two Complete Thoughts (Avoiding Comma Splices and Run-ons)

When you have two complete thoughts (called independent clauses in grammar terms) - meaning each part could stand alone as its own sentence - you need to separate them properly. You cannot join them with just a comma or no punctuation at all.

Test for a complete thought:

• Does it have a subject? (who/what is doing something)
• Does it have a verb? (the action)
• Does it express a complete idea?

If you have TWO complete thoughts, your options are:

1. Period (make two sentences):
   • Dr. Chen detected unusual frequencies. She determined they came from a neutron star.
2. Semicolon (if thoughts are closely related):
   • Dr. Chen detected unusual frequencies; she determined they came from a neutron star.
3. Comma + coordinating conjunction (FANBOYS: for, and, nor, but, or, yet, so):
   • Dr. Chen detected unusual frequencies, and she determined they came from a neutron star.

What DOESN'T work:

Comma alone (comma splice):

• Dr. Chen detected unusual frequencies, she determined they came from a neutron star.

No punctuation (run-on):

• Dr. Chen detected unusual frequencies she determined they came from a neutron star.

In this question:

• First complete thought: "she detected unusual radio wave frequencies in the observations"
• Second complete thought: "she determined the frequencies originated from a rapidly rotating neutron star"
• The tricky part: The prepositional phrase "With the application of signal filtering algorithms" might make you think the second part isn't complete, but it is! The phrase just adds information about HOW she determined something - the core sentence "she determined the frequencies originated..." is still complete.

Since we have two complete thoughts, we need a period to separate them, making choice B correct.