Human-made (synthetic) fibers used in clothes and many other consumer products are more durable than most natural plant _______ the...

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

• Human-made (synthetic) fibers
  • used in clothes and many other consumer products
• are more durable than most natural plant fibers [?]

• the manufacture of synthetic fibers
  • requires toxic chemical solvents
    • that can pollute air and water.

Understanding the Meaning

Let's start from the beginning and understand what this sentence is telling us:

'Human-made (synthetic) fibers used in clothes and many other consumer products are more durable than most natural plant fibers'

• This first part is making a comparison
  • Synthetic fibers last longer than natural plant fibers
  • This sounds like an advantage of synthetic fibers

Now we've reached the blank: 'fibers ______'

Let's look at the choices:

• A gives us just a comma
• B gives us "but" with no comma
• C gives us nothing at all
• D gives us a comma plus "but"

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

'the manufacture of synthetic fibers requires toxic chemical solvents that can pollute air and water'

• This second part tells us about a downside of synthetic fibers
  • Making them requires toxic chemicals
  • These chemicals can pollute air and water
  • This is clearly a negative aspect

So the complete picture is:

• First part: synthetic fibers are MORE durable (a positive)
• Second part: making them requires TOXIC, POLLUTING chemicals (a negative)

What do we notice about the structure here?

• Both parts are complete thoughts that could stand alone as sentences:
  • 'Human-made fibers...are more durable than most natural plant fibers.' ✓
  • 'The manufacture of synthetic fibers requires toxic chemical solvents...' ✓

• These two complete thoughts present contrasting ideas:
  • The first highlights an advantage
  • The second presents a disadvantage
  • The word "but" signals this contrast

• When we connect two complete thoughts with a word like "but," we need:
  • A comma before "but"
  • Then "but"
  • Then the second complete thought

So we need Choice D: fibers, but - the comma and "but" together properly connect these two contrasting complete thoughts.

GRAMMAR CONCEPT APPLIED

Connecting Two Complete Thoughts with Contrasting Ideas

When you have two complete thoughts (each with its own subject and verb that could stand alone as a sentence) and you want to connect them to show a contrast, you need a comma plus a contrasting word like "but" (called a coordinating conjunction in grammar terms):

Pattern: [Complete thought], but [complete thought].

Example 1:

• Complete thought 1: The movie was long
• Complete thought 2: It was entertaining
• Connected: The movie was long, but it was entertaining.

Example 2:

• Complete thought 1: She studied hard for the exam
• Complete thought 2: She still felt nervous
• Connected: She studied hard for the exam, but she still felt nervous.

In our question:

• Complete thought 1: Human-made fibers are more durable than most natural plant fibers
• Complete thought 2: the manufacture of synthetic fibers requires toxic chemical solvents that can pollute air and water
• Connected: ...more durable than most natural plant fibers, but the manufacture of synthetic fibers requires...

The comma is essential - without it (Choice B), the sentence violates punctuation rules. Using just a comma (Choice A) or nothing (Choice C) creates improper sentence structure.