前者. /u:/的口型很紧,张开很小（上下嘴唇相距1厘米）,双唇向前撅成一个小圆圈,与汉字“驴”的韵母口型很像.要是按照汉字“鲁”的韵母发就错了. To  make  the  /u:/  sound,keep  the  mouth  slightly  open  and  the  lips  1  cm  apart.The  lips  are  tense,and  pushed  forward  into  a  small  circle. 像/ju:/是错觉.
关于two的读音 教学时是发tu:还是tju:?谢谢!