One teacher tried to get her class to pronounce "fine" correctly. Over and over again she would repeat "fine", telling them, "Hit your lower lip with your upper teeth.
比如有一次，為了教「I am fine」中 “f” 的發音，謝老師清楚地教道：「上牙齒扣下嘴唇﹘ ﹘ F-ine！」