下列情况哪一种是皮脂腺囊肿所特有的表现
A.常见于面部
B.发生缓慢
C.囊壁与皮肤粘连,中央可有色素点
D.质地软,无压痛
E.边界清楚,可活动
参考答案:C
By the time you have completed the essential training, you ________ exposed to virtually
every new feature of the course.[ ]
A. will have been
B. are
C. have been
D. will be
简述经典性条件反射的形成。