@tayconlinh075: Explanation: After “Not only” at the beginning of a sentence, we use inversion. The auxiliary verb comes before the subject: Not only has the cost... The subject is “the cost”, which is singular, so we use “has,” not “have.” The structure is: Not only + auxiliary verb + subject + main verb... This structure is useful in formal English and can help create more sophisticated sentences in IELTS Writing. #EnglishGrammar #GrammarQuiz #AskTikTok #hashtag #LearnEnglish