1. Rules banning cancer-causing substances from food apply to new food additives and not to natural constituents of food because their use as additives is entirely avoidable.
(A) their use as additives is
(B) as additives, their use is
(C) the use of such additives is
(D) the use of such additives are（C）
(E) the use of them as additives is
请教这道题的句子结构是什么呀？我觉得没谓语呀？ | 
