In nontonal languages, intonation is a very important prosodic feature to distinguish sentence meanings. But in tonal languages, such as Mandarin Chinese, declarative and interrogative sentences both have falling intonation. In this case, interrogative sentences differ from the former by having a question particle in the final position of the sentence or a question word. At the prosodic level, what are the prosodic features which distinguish declarative and interrogative sentences, if these two types of sentences have similar intonational contour patterns? Following Lyons (1977) and Li & Thompson (1979), question words are the focus of questions in an interrogative sentence. They should have a phonetic, acoustic realization more important than other words in the sentence. However, in the primary study about the interrogative word ``ji'' with third tone (how many) in WH-question sentence, ``ji'' had a short duration, it had not undergone the 3-tone tone sandhi, and was realized as a neutral tone. This study will examine in detail the acoustic phonetic realizations of interrogative words, to find out their prosodic features and to know how listeners react to these features.