English文法 一些問題....請幫幫我

非常簡單：
food 係 uncountable noun，所以動詞係要用 be o既第三身單數形，即係 is。即使佢係o係 there 之後、food 之前，或者今次係問句中開頭，都係一樣，要同個名詞相配合。
pie 係 countable noun，你都用左複數用（pies），咁因為上述原因，動詞就要用 be o既複數形態，即係 are。
如果俾得你填／揀o既係 food 或者 pies 呢個字o既位，咁你揀答案就要留意到底動詞有冇俾貼士你。
圖片參考：http://tw.yimg.com/i/tw/ugc/rte/smiley_3.gif

這也可以「白馬非馬」的道理解釋的。
Food includes pies on the menu. It is very unlikely that you should limit your friend's choice in only one type of food, i.e. pies. Therefore, the first question is the right one to use.
But if your friend already mentioned she only wanted to try the PIES of that
particular restaurant, or she only wanted a PIE at that particular moment, the
second question would become the right one to use too.