问题
选择题
Food shortage will long be a worldwide problem _______ much has been done to supply enough for everyone.
A．before
B．if
C．since
D．although
答案
D
本题考查状语从句；虽然为满足每一个人的需求做了大量的工作，但食物缺乏仍然是一个长期的问题，所以选although。