a cake a cake of soap

a cake a cake of soap a piece of cake 为什么paper纸 a cake of soap一块肥皂等是不可数名词? a cake Just a piece of cake! a cake with lots of It's a piece of cake a piece of cake啥意思 a piece of cake=easy吗? a piece of cake就是小菜一碟? Have a t____ of this cake,please. Speaking English is a piece of cake.