To survive when water is scarce, embryos inside African turquoise killifish eggs _______ a dormant state known as diapause. In...

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

• To survive when water is scarce,
  • embryos inside African turquoise killifish eggs
    • [?] a dormant state known as diapause.
• In this state,
  • embryonic development
    • is paused for as long as two years—
      • longer than the life span of an adult killifish.

Understanding the Meaning

Let's start reading from the beginning:

'To survive when water is scarce,'

• This tells us the PURPOSE - why something happens
• It's setting up the reason for what comes next

'embryos inside African turquoise killifish eggs'

• These are the embryos we're talking about - the ones inside these specific fish eggs
• This is our SUBJECT - who/what does the action

Now here's where we need to fill in the blank:
'embryos inside African turquoise killifish eggs ______ a dormant state'

Let's look at our choices:

1. enter (base verb form)
2. to enter (infinitive form)
3. having entered (perfect participle)
4. entering (present participle)

What do we notice about what this sentence needs?

• We have our subject: "embryos"
• The opening phrase "To survive..." is just an introductory purpose phrase
• Now we need the MAIN ACTION of the sentence - the main verb that tells us what the embryos actually DO
• Looking at our choices:
  • "enter" is a complete verb form that can stand alone
  • "to enter" is an infinitive - it can't be the main verb by itself
  • "having entered" is a participle - it can't be the main verb by itself
  • "entering" is also a participle - it needs a helping verb like "are"

So we need enter - the only form that can serve as the main verb with our plural subject "embryos."

Now let's read the rest to see the complete picture:

'a dormant state known as diapause'

• This tells us WHAT they enter
• A dormant state = a resting, inactive state
• It's called "diapause"

The second sentence continues:
'In this state, embryonic development is paused for as long as two years—longer than the life span of an adult killifish.'

• This explains what happens in that dormant state
• Development stops/pauses
• It can last up to 2 years
• That's actually longer than how long adult killifish live!

So the complete picture: To survive when water is scarce, the embryos enter a dormant/resting state where their development pauses for up to 2 years.

The correct answer is A. enter.

GRAMMAR CONCEPT APPLIED

Finite vs. Non-Finite Verb Forms: Every Sentence Needs a Main Verb

Every complete sentence must have a finite verb - a verb form that can stand alone as the main verb and shows tense/agreement. Non-finite forms cannot do this job by themselves.

Finite forms (CAN be main verbs):

• Simple present/past: "The embryos enter the state" ✓
• With helping verbs: "The embryos are entering the state" ✓
• "The embryos have entered the state" ✓

Non-finite forms (CANNOT be main verbs alone):

• Infinitives: "The embryos to enter the state" ✗ (incomplete)
• Participles without helpers: "The embryos entering the state" ✗ (fragment)
• "The embryos having entered the state" ✗ (fragment)

In this question:

• Subject: "embryos" (plural)
• Need: finite main verb
• Only "enter" works as a finite verb with plural subject
• The other forms are all non-finite and would create sentence fragments

Key insight: When you see a subject followed by a blank, ask yourself: "Do I need the MAIN VERB here?" If yes, you need a finite form that can stand alone, not an infinitive or participle without a helping verb.