Formed in 1967 to foster political and economic stability within the Asia-Pacific region, the Association of Southeast Asian Nations was...

Sentence Structure

• Formed in 1967
  • to foster political and economic stability
    • within the Asia-Pacific region,
• the Association of Southeast Asian Nations
  • was originally made up of five members:
    • Thailand,
    • the Philippines,
    • Singapore,
    • Malaysia,
    • and Indonesia.

• By the end of the 1990s,
• the organization [?] its initial membership.

Understanding the Meaning

The first sentence gives us the background:

• 'Formed in 1967 to foster political and economic stability within the Asia-Pacific region'
  • This tells us when ASEAN was created and why
• 'the Association of Southeast Asian Nations was originally made up of five members'
  • So it started with just five countries
  • The list follows: Thailand, the Philippines, Singapore, Malaysia, and Indonesia

Now the second sentence tells us what happened later:

• 'By the end of the 1990s, the organization ______ its initial membership.'

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

• "has doubled" (present perfect)
• "had doubled" (past perfect)
• "doubles" (simple present)
• "will double" (future)

So we're deciding which verb tense fits here.

To see what works, let's think about the time relationships:

• The organization was formed in 1967 (past)
• Something happened to its membership
• We're measuring this at a specific point: "by the end of the 1990s" (also past)

What do we notice about "by the end of the 1990s"?

• This phrase is telling us about a specific past time point
• The word "by" means "before or at that time" - so the doubling was completed before or at the end of the 1990s
• We're looking back from a past moment (end of 1990s) at something that had already been completed

Here's the key relationship:

• When we talk about an action that was completed BEFORE a specific past time point, we need a verb tense that shows "past before past"
• That's what "had doubled" does - it shows the membership doubling was completed by that past reference point

So we need Choice B: "had doubled"

The sentence is saying: By the time we reached the end of the 1990s, the organization had already doubled from its original five members to ten.

GRAMMAR CONCEPT APPLIED

Using Past Perfect for Actions Completed Before a Past Reference Point

When you're talking about something that happened BEFORE another past event or past time, you use past perfect tense (called "had" + past participle in grammar terms):

The Pattern:

• Simple Past: describes actions at a past time
  • "In 2000, the company expanded its operations."
• Past Perfect: describes actions completed BEFORE another past time
  • "By 2000, the company had expanded its operations."
  • The expansion was already complete when we reached 2000

Key Signal Phrases that often require Past Perfect:

• "By [past time]" → "By 1995, they had launched three products"
• "Before [past event]" → "Before the meeting started, she had prepared the report"
• "When [past event]" → "When he arrived, the show had already begun"

In this question:

• "By the end of the 1990s" signals we need past perfect
• The doubling was completed at or before that past reference point
• Therefore: "had doubled" is correct