Even though bats prefer very sweet nectar, the plants that attract them have evolved to produce nectar that is only...

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

• Even though bats prefer very sweet nectar,
  • the plants that attract them
    • have evolved to produce nectar
      • that is only moderately sweet.

• A recent study [?] why:
  • making sugar is energy-intensive,
  • and it is more advantageous for plants
    • to make a large amount of low-sugar nectar
    • than a small amount of high-sugar nectar.

Understanding the Meaning

Let's start reading from the beginning.

The first sentence sets up an interesting puzzle:

• 'Even though bats prefer very sweet nectar'
  • Bats like nectar that's really, really sweet

• 'the plants that attract them have evolved to produce nectar that is only moderately sweet'
  • But the plants these bats visit actually make nectar that's only somewhat sweet – not as sweet as bats prefer

So there's a mismatch! Bats want super sweet nectar, but plants give them medium-sweet nectar. Why?

Now here's where we need to fill in the blank:

• 'A recent study ______ why:'

Let's look at our choices:

• explains (complete verb form)
• explaining (participle form)
• having explained (perfect participle)
• to explain (infinitive form)

What do we have so far?

• 'A recent study' is our subject – a singular thing
• We need a verb that tells us what the study does
• The study is telling us why this phenomenon happens

So we need a main verb – a complete verb form that goes with 'A recent study' and tells us the action it's performing.

The answer is: explains

• 'A recent study explains why' – the study is actively providing the explanation
• 'Explains' is the complete verb form that matches our singular subject 'A recent study'

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

• After the colon, we get the actual explanation:
  • 'making sugar is energy-intensive'
    • It takes a lot of energy for plants to make sugar

• 'and it is more advantageous for plants to make a large amount of low-sugar nectar than a small amount of high-sugar nectar'
  • Plants are better off making lots of medium-sweet nectar
  • Rather than spending all their energy making a tiny amount of super-sweet nectar

What do we notice about the structure here?

• 'A recent study' needs a main verb – the primary action word that tells us what the subject is doing

• 'Explains' serves as that main verb
  • It's a complete verb form (finite verb)
  • It agrees with the singular subject 'A recent study'
  • It tells us the action: the study is explaining something

• The other choices are different verb forms that cannot serve as the main verb of a sentence on their own:
  • 'explaining' is a participle – needs a helping verb
  • 'having explained' is a perfect participle – needs another main verb
  • 'to explain' is an infinitive – expresses purpose, not main action

So the correct answer is A. explains because it's the only form that works as the main verb matching our subject.

GRAMMAR CONCEPT APPLIED

Using Finite Verbs as Main Verbs

Every complete sentence needs a main verb in finite form – meaning a verb form that shows tense and agrees with the subject. This is different from non-finite forms (called participles, gerunds, and infinitives in grammar terms) which cannot stand alone as the main verb.

The pattern:

1. Finite verb (works as main verb):
   • The researcher discovers a new species.
   • "discovers" = complete verb, present tense, agrees with singular subject

2. Present participle (cannot work alone as main verb):
   • The researcher discovering a new species. (incomplete)
   • The researcher is discovering a new species. (needs helping verb)

3. Perfect participle (cannot work alone as main verb):
   • The researcher having discovered a new species. (incomplete)
   • The researcher, having discovered a new species, published her findings. (needs another main verb)

4. Infinitive (cannot work alone as main verb):
   • The researcher to discover a new species. (incomplete)
   • The researcher wants to discover a new species. (needs another main verb)

In our question:

• Subject: "A recent study" (singular, third person)
• Main verb needed: "explains" (finite form, present tense, third person singular)
• Complete sentence: "A recent study explains why..."

The key is recognizing that your subject needs a complete, finite verb form to create a grammatically complete sentence.