问题补充:
Food safety is one of the problemsnow all over the world.
A. discussed
B. to be discussed
C. being discussed
D. having been discussed
答案:
A. discussed
B. to be discussed
(答案→)C. being discussed
D. having been discussed
解析:考查分词做定语。本句中的动词discuss与名词problems之间构成被动关系,因为本句有now说明这个问题正在被讨论,用现在分词的被动语态。句意:现在食品安全是一个全世界都正在讨论的问题。故C正确。