Understanding Grammatical Correctness in Past Events

This question tests the correct usage of verb tenses when describing two actions that occurred in the past. Specifically, it focuses on the sequence of events. When two actions happen in the past, and one action occurred before the other, the earlier action is typically expressed using the Past Perfect tense (had + past participle), while the later action is expressed using the Simple Past tense (verb's past form).

Let's analyze the structure:

• Event 1 (Earlier): The train left.
• Event 2 (Later): We reached the station.

According to standard English grammar rules for sequencing past events, Event 1 should be in the Past Perfect tense, and Event 2 should be in the Simple Past tense.

Analyzing the Options

• Option 1:
  When we reached the station, the train have already left.

  This sentence is incorrect because the verb "have" is not appropriate here. "Train" is a singular subject, and the context requires a past tense. "Have" is used with plural subjects or 'I'/'you' in the present perfect tense, or as an auxiliary in other constructions, but not correctly here for a past event sequence.

• Option 2:
  When we reached the station, the train has already left.

  This sentence uses the Present Perfect tense ("has left"). While "reached" is in the Simple Past tense, using the Present Perfect for the first action is generally incorrect when both actions are clearly completed in the past and distinct from the present moment. The sequence requires the Past Perfect for the earlier action.

• Option 3:
  When we reached the station, the train had already left.

  This sentence correctly uses the Past Perfect tense ("had already left") for the action that happened earlier (the train leaving) and the Simple Past tense ("reached") for the action that happened later (us reaching the station). This structure accurately reflects the sequence of past events.

• Option 4:
  When we reached the station, the train already left.

  This sentence uses the Simple Past tense ("left") for both actions. While Simple Past can sometimes imply sequence, the word "already" combined with the need to clearly distinguish the earlier event makes the Past Perfect tense ("had already left") the grammatically preferred and more precise structure. The auxiliary verb "had" is missing.

Conclusion on Correct Tense Usage

The grammatically correct sentence is the one that properly employs the Past Perfect tense to indicate the action that happened first in the past.

Correct Structure: Simple Past (later action), Past Perfect (earlier action).

Therefore, the sentence "When we reached the station, the train had already left." is the correct one.