Apple and peach is my favorite fruit(改错)

Apple and peach are my favourite fruit这句话中是两种不同种类的水果，所以用复数形式are
Bread and butter is their daily food这句话中按西方的传统观点，抹上黄油的面包已经是一种约定俗成的食物了，所以用单数形式。比如Knife and fork is the tableware in the West(刀叉是西方世界的餐具）
又比如That singer and dancer is my friend(那个歌手兼舞者是我朋友）That singer and that dancer are my friends(那个歌手和那个舞者都是我朋友）

Apple and peach are my favorite fruits.

Apple and peach are my favorite fruit.可数名词be动词变复数。

Bread and butter is their daily food.不可数名词be动词用单数形式。

第一句的“is"改成"are"(因为APPLE和PEACH都是可数名词，用AND连接就是复数

第二句两个单词都是不可数名词，放一起还是不可数的，所以be动词用单数形式

Apples and peaches are my favourite fruits.

Apple and peach is my favorite fruit.错在主语是两个可数名词的单数，那么该主语就变成了复数，而系动词却用了单数。所以应该将"is"改成"are",将"fruit"改成"fruits".
Bread and butter are their daily food.这里的主语是Bread and butter，意思是“面包夹黄油”，主语是单数，系动词用复数就矛盾了，所以应该将"are"改成"is".