They all appeared ___ this song before.

A．to learn

B．to have learned

C．to not have learned

D．not learning from

患者男，10岁，因前牙排列不齐、有间隙，来医院检查，发现口内乳牙和恒牙都存在，对于其关系的判断，不是暂时性错的为（）

A.中切牙间存在间隙

B.恒侧切牙向侧方倾斜

C.上下第一恒磨牙，出现偏远中关系

D.下颌前牙位于上颌前牙的唇侧

E.上前牙拥挤