Each year in the fall, when the weather starts to cool in the northern hemisphere, millions of North American monarch...

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

Sentence 1:

• Each year in the fall,
  • when the weather starts to cool in the northern hemisphere,
• millions of North American monarch butterflies
  • journey south.

Sentence 2:

• Searching for food and warmer habitats,
• they
  • [?] thousands of miles
    • —from as far north as Canada all the way down to Mexico—
  • on this annual migration.

[Where the blank varies: flew/were flying/had flown/fly]

Understanding the Meaning

Let's start by reading the first sentence:

'Each year in the fall, when the weather starts to cool in the northern hemisphere, millions of North American monarch butterflies journey south.'

What does this tell us?

• 'Each year'
  • signals that we're talking about something that happens repeatedly
  • this is a recurring pattern, not a one-time event
• 'starts' and 'journey'
  • both are present tense verbs
  • they're describing what happens regularly, year after year

This is where we have the blank. Let's look at the choices - they're asking us to pick the right verb tense: flew, were flying, had flown, or fly.

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

'Searching for food and warmer habitats, they ______ thousands of miles—from as far north as Canada all the way down to Mexico—on this annual migration.'

Now let's understand what this is telling us:

• 'Searching for food and warmer habitats'
  • explains why the butterflies travel
• 'they ______ thousands of miles'
  • describes the journey distance
  • 'they' refers to the butterflies
• 'from as far north as Canada all the way down to Mexico'
  • gives specific geographic details of the journey
• 'on this annual migration'
  • 'annual' means yearly
  • confirms this happens every single year

So the complete picture is:

• The passage describes what monarch butterflies do every year as a regular pattern
• They travel south each fall, covering thousands of miles

What do we notice about the verb tense pattern?

• The first sentence uses present tense verbs - 'starts' and 'journey'
  • These describe what happens regularly, year after year
• The phrase 'Each year' tells us we're describing a habitual action
  • Not something that happened once in the past
  • But something that happens repeatedly as an ongoing pattern
• When we describe actions that happen regularly or habitually, we use present tense
  • This shows it's a continuing pattern, not a past event

The correct answer is D (fly).

The verb needs to be in present tense to match 'starts' and 'journey' and to properly describe this recurring annual event.

GRAMMAR CONCEPT APPLIED

Using Present Tense for Habitual and Recurring Actions

When we describe actions that happen regularly, habitually, or as general patterns (rather than one-time events), we use present tense. This is especially true when the passage includes time markers like "each year," "every day," "annually," or "regularly."

Pattern Recognition:

Time Signal + Present Tense = Habitual Action

Example 1:

• "Every morning, the sun rose in the east."
• "Every morning, the sun rises in the east."
  • "Every morning" signals a recurring pattern
  • Present tense "rises" shows this happens regularly

Example 2:

• "Each semester, students registered for classes."
• "Each semester, students register for classes."
  • "Each semester" indicates a repeating event
  • Present tense "register" describes the ongoing pattern

In Our Question:

• Time signal: "Each year" and "annual migration"
• Established pattern: "starts" and "journey" (both present tense)
• Blank needs: "fly" (present tense) to maintain consistency and describe the recurring action

The key is recognizing that when a passage describes what happens regularly as an ongoing pattern, all verbs describing that pattern should be in present tense—even if the event involves movement or travel that might seem "past" at any given moment.