In the 6th Grade ICSE English textbook, students learn about different types of sentences, such as declarative, interrogative, imperative, and exclamatory sentences. The question "xfcvdcvfv" does not form a complete sentence and does not fall into any of these categories. It appears to be a random combination of letters without any meaning in English. In order to form a proper sentence, it is important to use correct grammar and punctuation.