sheep 是单复数同形，表示单数时用is， 复数时用are。
sheep n.羊；绵羊
The island is populated largely by sheep.
这个岛的`主要生物是绵羊。
The minister preached a sermon on the parable of the lost sheep.
牧师讲道时用了亡羊的比喻。
The first task was to fence the wood to exclude sheep
第一项任务就是把树林围起来不让羊进去。
