Understanding Verb Tenses in Sentence Correction

The question asks us to identify the most appropriate substitution for the underlined segment "has allowed" in the sentence: "In 1920s, new technology has allowed filmmakers to attach to each film a soundtrack of speech."

Let's analyze the sentence structure and the time reference.

• The sentence begins with the phrase "In 1920s". This clearly indicates a specific period in the past.
• The underlined verb phrase is "has allowed". This is in the present perfect tense.

The present perfect tense is typically used for:

• Actions that started in the past and continue to the present.
• Actions that happened at an unspecified time in the past.
• Actions that happened in the past but have a result or connection to the present.

However, when a specific past time is mentioned (like "In 1920s"), the simple past tense is generally used for completed actions. The action of the technology allowing filmmakers to add sound happened and was completed within that specific past period (the 1920s).

Let's evaluate the given options:

1. allowed: This is the simple past tense of "allow". The simple past tense is used for actions that happened and were completed at a specific time in the past. This perfectly matches the time reference "In 1920s".
2. has allowed: This is the present perfect tense. As explained above, the present perfect is not appropriate when a specific past time like "In 1920s" is given.
3. was allowed: This is the simple past passive voice. The original sentence implies that the technology was the agent performing the action (technology allowed), not that the technology was allowed by something else. The active voice is more appropriate here.
4. No substitution required: This would imply the original sentence is correct. However, the use of the present perfect ("has allowed") with the specific past time reference ("In 1920s") is grammatically incorrect.

Therefore, the simple past tense verb "allowed" is the most suitable option to replace "has allowed" to correctly reflect that the action took place during the specific past period mentioned.

The corrected sentence would be: "In 1920s, new technology allowed filmmakers to attach to each film a soundtrack of speech."

Revision Table: Verb Tenses and Time References

Additional Information: Simple Past vs. Present Perfect

Understanding the difference between the simple past and present perfect tenses is crucial for correct sentence construction, especially when time adverbs are involved. The simple past tense is used to talk about actions that are finished and happened at a definite time in the past. The exact time might be mentioned (e.g., "last year," "three days ago," "in 1950") or understood from the context. The focus is on the completed action in the past.

The present perfect tense, on the other hand, connects the past to the present. It can describe an action that began in the past and continues now, an action that happened at an indefinite time before now, or a past action whose result is relevant now. Adverbs like 'just', 'already', 'yet', 'ever', 'never', 'since', and 'for' (when referring to a duration up to the present) are often used with the present perfect. However, if 'for' or 'since' is used with a specific past time adverbial that indicates a completed period (e.g., 'for five years in the 1920s'), the simple past might still be appropriate.

In the given sentence, "In 1920s" is a specific past time period, clearly indicating when the action of the technology allowing filmmakers to add sound occurred. Therefore, the simple past tense "allowed" is the correct choice.