Read the given sentence in indirect speech and select the option that correctly converts it into direct speech.

She mentioned that they had completed the assignment before she arrived.

To convert the given sentence from indirect speech to direct speech, let us analyze the tense structure and pronouns used in indirect speech:
Indirect speech: She mentioned that they had completed the assignment before she arrived.

Step 1: Identify the Reporting Verb and Main Structure
The reporting verb is "mentioned". In direct speech, the reported clause will be enclosed within quotation marks, followed or preceded by the reporting clause: "... ," she mentioned.

Step 2: Convert Pronouns
- The pronoun "they" remains "they" in direct speech since it refers to third-person plural.
- The pronoun "she" in the time clause "before she arrived" refers to the speaker ("I" in direct speech).

Step 3: Determine the Tense Changes
- In the indirect speech clause "they had completed ... before she arrived", the past perfect tense ("had completed") indicates an action that was already completed before another past event ("before she arrived").
- In direct speech, when expressing two past actions where one occurred before another, the past perfect ("had completed") and simple past ("arrived") remain accurate in maintaining the sequence of time relative to the speaker's statement.
- Therefore, "they had completed the assignment before I arrived" directly corresponds to what was spoken by her.

Step 4: Verify with the Options
Comparing with the given options:
- Option 1: “They had completed the assignment before I arrived,” she mentioned. (Correct)
- Option 2: Uses "have completed" which changes the meaning.
- Option 3: Uses "completed" which drops the past perfect distinction.
- Option 4: Incorrectly uses "had arrived" for the second action.

Thus, the correct direct speech sentence is:
“They had completed the assignment before I arrived,” she mentioned.