Working from an earlier discovery of Charpentier's, chemists Emmanuelle Charpentier and Jennifer Doudna—winners of the 2020 Nobel Prize in Chemistry—r...

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

• Working from an earlier discovery of Charpentier's,
  • chemists Emmanuelle Charpentier and Jennifer Doudna
    • —winners of the 2020 Nobel Prize in Chemistry—
  • re-created and then reprogrammed
    • the so-called 'genetic scissors'
      • of a species of DNA-cleaving bacteria
  • ______ (?)
    • a tool
      • that is revolutionizing the field of gene technology.

Understanding the Meaning

Let's start reading and understanding from the beginning:

'Working from an earlier discovery of Charpentier's'

• This sets up the starting point - they're building on earlier work.

'chemists Emmanuelle Charpentier and Jennifer Doudna'

• These are the people doing the action - our main subjects.
• The sentence gives us extra information about them:
  '—winners of the 2020 Nobel Prize in Chemistry—'

're-created and then reprogrammed'

• These are the main actions - what the chemists did.
• First they re-created something, then they reprogrammed it.

'the so-called 'genetic scissors' of a species of DNA-cleaving bacteria'

• This is what they worked with - genetic scissors from bacteria that can cut DNA.

This is where we have the blank.

Let's look at our choices:

• A. to forge
• B. forging
• C. forged
• D. and forging

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

The sentence continues: 'a tool that is revolutionizing the field of gene technology.'

Now let's understand what this complete sentence is telling us:

• The chemists took these genetic scissors
  • re-created them and reprogrammed them
• The result of this work was 'a tool that is revolutionizing the field'
  • So their re-creating and reprogramming wasn't the end goal
  • They did those actions FOR A PURPOSE - to create/forge this tool

What do we notice about the structure here?

• We have the main actions already stated: 're-created and then reprogrammed'
  • These are the complete main verbs of the sentence
• After stating what they did, we need to express WHY they did it
  • What was the purpose of their re-creating and reprogramming?
  • Answer: to forge a tool
• When we want to express the PURPOSE or GOAL of an action, we use the infinitive form: 'to + verb'
  • They re-created and reprogrammed [for what purpose?] → TO FORGE a tool

So we need A. to forge - this infinitive form shows the purpose or goal of their work.

GRAMMAR CONCEPT APPLIED

Using Infinitives to Express Purpose

When you want to show that someone performed an action in order to accomplish a particular goal, you use an infinitive (called an infinitive of purpose in grammar terms) - the "to + verb" form:

Pattern: [Main action] + to + verb [the goal/purpose]

Example 1:

• Scientists conducted experiments to discover a cure
  • Main action: conducted experiments
  • Purpose: to discover a cure

Example 2:

• The company invested millions to develop new technology
  • Main action: invested millions
  • Purpose: to develop new technology

In our question:

• Main actions: re-created and reprogrammed the genetic scissors
• Purpose: to forge a tool that is revolutionizing gene technology

The infinitive "to forge" clearly expresses that forging the tool was the purpose or goal of their re-creating and reprogramming work.