In 2021, Mexican biologist Martha Lydia Macías-Rubalcava led a review of the scientific literature related to endophytic fungi (i.e., fungi...

Let's begin by understanding the meaning of this sentence. We'll use our understanding of pause points and segment the sentence as shown - understanding and assimilating the meaning of each segment bit by bit!

Sentence Structure

• In 2021,
  • Mexican biologist Martha Lydia Macías-Rubalcava
  • led a review
    • of the scientific literature
      • related to endophytic fungi
        • (i.e., fungi that live inside a host plant) [?]
• [?] researching 120 endophytic fungi–produced compounds,
  • she
    • found
      • that their phytotoxicity can make them viable alternatives
        • to chemical herbicides
          • for controlling weeds.
  • Where [?] = ). By OR ), by OR ) and by OR ) by

  Understanding the Meaning

  Let me start by reading from the beginning:

  "In 2021, Mexican biologist Martha Lydia Macías-Rubalcava led a review of the scientific literature related to endophytic fungi"

  • This tells us what the biologist did - she led a review (a comprehensive examination) of scientific literature
  • The literature was about endophytic fungi

  The sentence adds a helpful clarification in parentheses:

  • "(i.e., fungi that live inside a host plant)"
  • This explains what "endophytic fungi" means - they're fungi that live inside plants

  This is where we have the blank.

  Let's look at the choices:

  • A: ). By (period after parenthesis, capital B)
  • B: ), by (comma after parenthesis, lowercase b)
  • C: ) and by (no punctuation, includes "and")
  • D: ) by (no punctuation, lowercase b)

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

  "[blank] researching 120 endophytic fungi–produced compounds, she found that their phytotoxicity can make them viable alternatives to chemical herbicides for controlling weeds."

  Now let's understand what this is telling us:

  • "By researching 120 endophytic fungi–produced compounds"
    • This phrase explains HOW she arrived at her finding
    • She researched compounds that are produced by these endophytic fungi
  • "she found that their phytotoxicity can make them viable alternatives to chemical herbicides"
    • Subject: she
    • Main verb: found
    • What she found: these compounds' phytotoxicity (ability to be toxic to plants) makes them potentially useful as herbicides to control weeds

  So the complete picture is:

  • First part: Martha Lydia Macías-Rubalcava led a review of scientific literature about endophytic fungi
  • Second part: By doing research on 120 compounds, she found these compounds could work as herbicides

  What do we notice about the structure here?

  Let me check each part:

  • "In 2021, Mexican biologist Martha Lydia Macías-Rubalcava led a review of the scientific literature related to endophytic fungi (i.e., fungi that live inside a host plant)"
    • Subject: Martha Lydia Macías-Rubalcava
    • Verb: led
    • This expresses a complete thought - it can stand alone as a sentence
  • "By researching 120 endophytic fungi–produced compounds, she found that their phytotoxicity can make them viable alternatives to chemical herbicides for controlling weeds"
    • Subject: she
    • Main verb: found
    • This also expresses a complete thought - it can stand alone as a sentence

  So we have TWO complete sentences (two independent clauses that can each stand alone).

  When you have two complete sentences, they must be properly separated. You cannot just:

  • Join them with only a comma (that creates a comma splice - incorrect)
  • Run them together with no punctuation (that creates a run-on - incorrect)

  You need to either:

  • Separate them with a period to make two sentences
  • Use a semicolon
  • Use a comma plus a coordinating conjunction like "and" or "but"

  The correct answer is Choice A: plant). By

  This properly separates the two complete sentences with a period, and capitalizes "By" because it starts a new sentence.

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  GRAMMAR CONCEPT APPLIED

  Separating Complete Sentences (Independent Clauses)

  When you have two complete sentences - each with its own subject and verb, expressing complete thoughts that could stand alone - you must separate them properly. These are called independent clauses in grammar terms.

  Three correct ways to handle two independent clauses:

  1. Use a period (create two separate sentences):
     • Sentence 1: The experiment yielded surprising results.
     • Sentence 2: The team published their findings immediately.
  2. Use a semicolon:
     • The experiment yielded surprising results; the team published their findings immediately.
  3. Use a comma + coordinating conjunction (FANBOYS: for, and, nor, but, or, yet, so):
     • The experiment yielded surprising results, and the team published their findings immediately.

  Two INCORRECT approaches (avoid these):

  1. Comma splice - joining with only a comma:
     • The experiment yielded surprising results, the team published their findings immediately.
  2. Run-on sentence - no punctuation:
     • The experiment yielded surprising results the team published their findings immediately.

  How this applies to our question:

  In our passage, we have:

  • First complete sentence: "Martha Lydia Macías-Rubalcava led a review of the scientific literature related to endophytic fungi (i.e., fungi that live inside a host plant)"
  • Second complete sentence: "By researching 120 endophytic fungi–produced compounds, she found that their phytotoxicity can make them viable alternatives to chemical herbicides for controlling weeds"

  These must be properly separated. The correct answer uses a period to create two distinct sentences, with "By" capitalized as the beginning of the second sentence.