The Hubble Space Telescope has transformed our understanding of the universe since its launch in 1990. Among its most significant...

Sentence Structure

• The Hubble Space Telescope has transformed our understanding of the universe since its launch in 1990.
• Among its most significant contributions
  • is the deep field image,
    • a photograph (?) reveals thousands of galaxies
      • in what appears to the naked eye as an empty patch of sky,
    • providing evidence
      • that the universe contains billions of galaxies beyond our own.

Understanding the Meaning

The first sentence gives us context:

• The Hubble Space Telescope has transformed our understanding of the universe since its launch in 1990.
  • This sets up that we're talking about Hubble's important contributions.

Now the second sentence tells us about one specific contribution:

• 'Among its most significant contributions is the deep field image'
  • So there's something called the "deep field image" that's really important.

The sentence continues by telling us more about what this deep field image is:

• 'a photograph...'
  • Okay, so the deep field image is a photograph.

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

• photograph that
• photograph,
• photograph
• photograph, that

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

• '...reveals thousands of galaxies in what appears to the naked eye as an empty patch of sky'
  • So this photograph shows us thousands of galaxies in a spot that looks empty to our eyes
  • This is explaining what makes THIS photograph special - what it does, what it reveals
• 'providing evidence that the universe contains billions of galaxies beyond our own'
  • And this discovery provides proof about how many galaxies exist

Now, what do we notice about the structure here?

• The phrase "reveals thousands of galaxies..." is describing the photograph
  • But it's not just adding extra information
  • It's telling us WHICH photograph we're talking about - the one that reveals these galaxies
  • This is essential, identifying information
• "Reveals" is a verb that needs to connect properly to its subject "photograph"
  • We need a word that links the noun "photograph" to the action "reveals"
• When we have a clause that provides essential information about which specific thing we mean:
  • We use "that" to connect it
  • We do NOT use a comma before "that"
  • The information is restrictive - it restricts which photograph we're talking about

So we need: photograph that

The correct answer is Choice A.

GRAMMAR CONCEPT APPLIED

Connecting Essential Modifying Information to Nouns

When you want to add a clause that tells you WHICH specific thing you're talking about - information that's essential to identifying the noun - you connect it with "that" and no comma. This is called a restrictive relative clause in grammar terms.

Pattern for Essential (Restrictive) Information:

• Noun + that + essential identifying information (NO comma)
• Example: "The book that changed my perspective was written in 1960."
• "that changed my perspective" tells you WHICH book
• Without this information, you wouldn't know which book is meant
• This is essential, so: that + no comma

Pattern for Extra (Non-Restrictive) Information:

• Noun + , which + extra information
• Example: "My favorite book, which was written in 1960, changed my perspective."
• "My favorite book" already identifies which book
• "which was written in 1960" just adds bonus details
• This is extra, so: which + comma

In this question:

• "a photograph that reveals thousands of galaxies"
• "that reveals thousands of galaxies" is essential - it identifies WHICH photograph
• The revealing of galaxies is what makes this particular photograph significant
• This is restrictive/essential information
• Therefore: that with no comma

Key principle: If you can remove the information and still know which specific thing is meant, use "which" with a comma. If removing it would make the noun too vague or unclear, use "that" with no comma.