请教如何算是造成句子结构分裂呢？

Judging from safety hazards, pickups and sport utility vehicles pose greater risks on the road than do cars an association of large insurance companies concluded.

(B) Pickups and sport utility vehicles pose greater risks on the road than do cars, judging from safety hazards, an association of large insurance companies concluded.

(C) An association of large insurance companies concluded, judging from safety hazards, that pickups and sport utility vehicles pose greater risks on the road than do cars.

(D) Judging from safety hazards, an association of large insurance companies concluded that pickups and sport utility vehicles pose greater risks on the road than do cars.

(E) Pickups and sport utility vehicles pose greater risks on the road than do cars, an association of large insurance companies concluded, judging from safety hazards.

答案是写 (D)

而 (C) 选项的错误说明为：将judging from safety hazards 放在 concluded 与 that 中间造成句子的分裂。

我的问题是(C)中，若将judging from safety hazards看成修饰前句，为什么不对呢？ 什么情况插入句会造成「结构分裂」呢？