The error in the sentence "He asked that why I was late" is B: that. When reporting questions indirectly, especially those introduced by a 'wh-word' (like who, what, where, when, why, how), we do not use the conjunction "that." The 'wh-word' itself acts as the conjunction, introducing the reported clause. Using "that" creates redundancy and is grammatically incorrect in this context.
The verb "asked" correctly introduces an indirect question. The word "why" correctly introduces the content of the question, and the clause "I was late" maintains the correct word order for an indirect question (subject-verb, not inverted like a direct question). Therefore, the correct way to phrase this sentence is "He asked why I was late." This structure is essential for forming grammatically sound reported speech, ensuring clarity and avoiding unnecessary words. Removing "that" makes the sentence flow naturally and adhere to standard English grammar rules for indirect questions.