knife是可數(shù)名詞還是不可數(shù)名詞

　　例句：

　　Bread knives should have a serrated edge.

　　面包刀的刀刃應帶有波浪齒。

　　Two knife racks hold her favourite knives.

　　兩個刀架上放著她最喜愛的刀。

　　2 000 knives have been handed in during the month-long amnesty.

　　在一個月的赦免期中交出了2 000把刀。