Liu Fang is a company CEO now, but she ____ as a teacher in a middle school for three years.

A．worked

B．has worked

C．works

D．had worked

家禽维生素A缺乏时，下述说法不正确的是：（）

A.口腔、咽、食道和嗉囊黏膜上有白色小结节

B.生长发育不良

C.在饲料中添加鱼肝油会加重病情

D.会发生视觉障碍