Food safety is one of the problemsnow all over the world.A. discussedB. to be discussed C.

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。