Which of the following sentences contains an adverbial error?

Correct option is A

Option (a) contains an error.
Explanation: “Clear” and “concise” are adjectives. Since the verb is “spoke,” adverbs should be used — “clearly and concisely.”
Grammatical rule used: Adverbs modify verbs and should be used in speech contexts.
Example: She spoke clearly and confidently at the seminar.