绵羊是不是可数名词?

　　例句：

　　They kept a small flock of sheep.

　　他们养了一小群绵羊。

　　The field had been grazed by sheep.

　　这块地羊已经啃过了。

　　This wool comes from goats, not sheep.

　　这种羊毛是山羊毛，不是绵羊毛。