Understanding Sentence Improvement Questions

Sentence improvement questions ask you to find the best way to phrase an underlined part of a sentence. Sometimes, the original sentence is already correct, and no change is needed. This type of question tests your knowledge of grammar, verb tenses, vocabulary, and sentence structure.

Analyzing the Sentence and Underlined Segment

The given sentence is: "Over the past 20 years, there has been a constant decline in the variety of vegetables that we eat because the native varieties are no longer available."

The underlined segment is "there has been". We need to evaluate if this phrase is correctly used in the context of the sentence, particularly with the time phrase "Over the past 20 years".

Examining the Verb Tense: "has been"

The phrase "has been" uses the present perfect tense (has/have + past participle). The present perfect tense is often used to describe an action or state that started in the past and continues up to the present, or a past action with a result in the present. The phrase "Over the past 20 years" indicates a period of time that began 20 years ago and extends continuously up to the current moment.

Let's consider why the present perfect "has been" is suitable here:

• It indicates a state (a constant decline) that began in the past (20 years ago) and is still relevant or ongoing in the present.
• The duration "Over the past 20 years" strongly suggests a connection between the past and the present, which is exactly what the present perfect tense conveys.

Evaluating the Options for Substitution

Let's look at the provided options:

1. No improvement:

   This option suggests the original sentence is correct. As discussed, "there has been" is appropriate with "Over the past 20 years" to show a decline that started in the past and continues or has results in the present.

2. is being:

   Using "there is being a constant decline" is grammatically incorrect in this context. The structure "is being" is typically used for the present continuous passive voice (e.g., "A house is being built") or to describe temporary behaviour ("He is being rude"). It is not used to describe a prolonged state or trend like a decline over 20 years.

3. was been:

   This combination of auxiliary verbs ("was" and "been") is grammatically incorrect in English. "Was" is the simple past tense of 'be', and "been" is the past participle. You would say "there was" (simple past) or "there had been" (past perfect), but not "was been".

4. had been:

   Using "there had been a constant decline" employs the past perfect tense. The past perfect is used to describe an action that happened before another action in the past. For example, "By 2020, there had been a decline over the previous 20 years." However, the phrase "Over the past 20 years" naturally connects to the present, making the present perfect ("has been") the more suitable tense unless there is another past event mentioned that the decline happened before.

Conclusion on Sentence Improvement

Comparing the options, the original phrase "there has been" correctly uses the present perfect tense to describe a constant decline over a period leading up to the present time ("Over the past 20 years"). None of the alternative options provide a grammatically correct or contextually appropriate substitution.

Therefore, no improvement is needed for the underlined segment.

Revision Table: Verb Tenses in English

Additional Information: Using "Over the past..."

The phrase "Over the past..." or "In the last..." followed by a period of time (e.g., "over the past few years", "in the last decade", "over the past 20 years") is a strong indicator that the present perfect tense (simple or continuous) is required. This is because these phrases describe a duration that starts in the past and continues right up to the present moment, linking the past experience or state directly to the present.

Examples:

• The climate has changed significantly over the past century.
• She has been studying hard in the last few months.
• There have been many advancements in technology over the past decade.

Using the past simple or past perfect with such phrases would typically be incorrect unless the context specifically places the entire duration and its effects entirely in the past relative to another past point.