sheep前面可以加a吗

前面可以加a，例如：

1、There is a sheep under the tree.树下有一只绵羊。

2、A goat is different from a sheep.山羊与绵羊不一样。

3、The path was no better than a sheep track.那条小路简直就像是羊肠小道。

4、I'd kinda like to have a sheep farm in New Mexico.我有点儿想在新墨西哥州开一个牧羊场。