Directions: The sentence below is split into four segments labelled (A), (B), (C), and (D). One segment contains a grammatical error. Identify the segment with the error.
It was exceptionally careless about the supervisor to have authorized five million dollars for such an unvetted vendor.

The correct answer is careless about the supervisor to.

Step-by-Step Breakdown:

1. Identify the Sentence Structure:
The given sentence follows the pattern: It + be + [adjective] + [preposition] + [person] + to-infinitive.

2. Grammar Rule: Prepositions with Adjectives of Behavior
When an adjective describes a personal quality, behavior, or character trait demonstrated by someone in performing an action, it must be followed by the preposition "of", not "about".
• Correct usage examples: "It was kind of you," "It was foolish of him," "It was careless of the supervisor."

3. Correction:
The segment "careless about the supervisor to" contains a prepositional error. The preposition "about" should be replaced with "of".
• Incorrect: "It was exceptionally careless about the supervisor to have authorized..."
• Correct: "It was exceptionally careless of the supervisor to have authorized..."

4. Analyzing the Remaining Segments:
• "It was exceptionally": The adverb "exceptionally" correctly modifies the adjective "careless".
• "have authorized five million": The perfect infinitive ("to have authorized") is correctly used to show that the action of authorizing happened prior to the observation.
• "dollars for such an unvetted vendor.": The phrase is grammatically sound, using "such an" appropriately with the singular countable noun phrase "unvetted vendor".