All samples from last week's production run, which lasted seventy-two consecutive hours, _____ examined by quality control specialists.

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

• All samples from last week's production run,
• which lasted seventy-two consecutive hours,
• [?] examined by quality control specialists.

Understanding the Meaning

Let me start reading from the beginning to understand what this sentence is saying.

'All samples from last week's production run'

• This tells us the subject - we're talking about samples
• Specifically, samples from a production run that happened last week
• 'All samples' - this is a plural subject (more than one sample)

'which lasted seventy-two consecutive hours'

• This gives us extra information about that production run
• It tells us how long it lasted - 72 hours straight
• Notice 'lasted' is past tense - this already happened

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

• 'All samples... ______ examined by quality control specialists'

Let's look at our choices:

• They're all forms of helping verbs that would work with 'examined'
• We're choosing between:
  • was (singular, past)
  • have been (plural, present perfect)
  • are (plural, present)
  • were (plural, past)

Based on what I've read so far, what do I need?

For agreement (matching the subject):

• My subject is 'All samples' - that's PLURAL
• So I need a plural verb
• This rules out 'was' (singular)

For tense (matching the time frame):

• 'last week's production run' - clearly in the past
• 'which lasted' - past tense confirms this happened in the past
• So I need a past tense verb
• This rules out 'are' (present) and 'have been' (present perfect)

So we need were - it's plural (matches 'samples') and past tense (matches 'last week's' and 'lasted').

The complete sentence tells us: All the samples from last week's production run (which went on for 72 consecutive hours) were examined by quality control specialists.

GRAMMAR CONCEPT APPLIED

Subject-Verb Agreement with Tense Consistency

When choosing the correct verb form, you need to check TWO things:

1. NUMBER AGREEMENT - Does the verb match the subject?

• Identify the true subject (the main noun doing or receiving the action)
• Don't be distracted by words in descriptive phrases
• Match your verb to whether the subject is singular or plural

In this sentence:

• Subject: "All samples" (plural)
• Not "production run" (that's in a descriptive phrase)
• Need: plural verb (were, not was)

2. TENSE CONSISTENCY - Does the verb match the time frame?

• Look for time markers (like "last week's," "yesterday," "currently")
• Look at other verbs in the sentence
• Keep your tenses consistent with the established time frame

In this sentence:

• Time marker: "last week's production run" (past)
• Other verb: "lasted" (past tense)
• Need: past tense verb (were, not are or have been)

Why both matter here:

• "All samples... were examined" ✓ (plural + past)
• "All samples... was examined" ✗ (singular + past) - number error
• "All samples... are examined" ✗ (plural + present) - tense error
• "All samples... have been examined" ✗ (plural + present perfect) - tense error