David was born _____. [ ]

A. since twenty years ago

B. for twenty years

C. twenty years ago

D. just over twenty years

关于子宫平滑肌瘤的叙述，下列哪项是错误的（）。

A.女性生殖系统中最常见的肿瘤

B.肿瘤边界清楚，但常无包膜

C.可发生黏液变性

D.瘤组织呈编织状排列

E.常发生恶变