E by buying prepared food
F the popularization of convenience food
5 Many people agree that food prices have increased sharply but they have failed _____
分析：直接根据搭配语法判断答案可能出自D或B。fail to do sth./没有做。。；而再根据搭配句意判断D最合适。
补充：
Failure n.失败, 失败的人, 故障, [美]不及格, 不履行; 疏忽
e.g. failure of electricity/ power failure停电
e.g. engine failure发动机失灵
e.g. failure to keep a promise失约
A Nor have the middlemen
B to increase the prices for food
C that they cannot agree on the causes of the increase in prices
E by buying prepared food
F the popularization of convenience food
1. The farmers have not been benefited very much， __________.
分析：根据空格前句的句意和语法特点（nor与 not连用，引导出另一分句），判断A正确。
补充：
Nor conj（与neither连用）也不; （与 not连用）也不；又不
e.g. Neither he nor his friends came back. 他和他的朋友都没有回来。
e.g. I dont want to go, nor will I. 我不想去，也不会去。
B to increase the prices for food
C that they cannot agree on the causes of the increase in prices
E by buying prepared food
F the popularization of convenience food
2. Housewives have to pay for the time they save_____________.
分析：根据搭配句意选择E（E作状语）。
B to increase the prices for food
C that they cannot agree on the causes of the increase in prices
F the popularization of convenience food
3. The economists have come to the conclusion that the cause of increased food prices lies in ____________.
分析：根据语法：介词后要跟名词性结构，不能直接跟从句结构。因此F合适