一盒粉笔是a box of chalk 还是 a box of chalks ?

一盒粉笔是a box of chalk 还是 a box of chalks ? 关于chalk一支粉笔是a piece of chalk那么一盒粉笔是a box of chalk 还是 a box o 一盒蛋糕是a box of cake还是a box of cakes?为什么 I want to buy a large box of chalks. I want a large box of chalk 和 I want a large box of the chal She ____(buy) a box of chalk yesterday And I want a large box of chalk ,too. The teacher picks up a __ of chalk from the chalk box. there are ____(一盒巧克力)on the table.,一盒巧克力是：a box of chocolate a box of 填入句中所缺的词 The teacher picks a ___ of chalk from the chalk box And I want a large box of chalk,too. 有and为什么还要加too