In the past, most children who went sledding in the winter snow in Verland used wooden sleds with runners and steering bars. Ten years ago, smooth plastic sleds became popular; they go faster than wooden sleds but are harder to steer and slow. The concern that plastic sleds are more dangerous is clearly borne out by the fact that the number of children injured while sledding was much higher last winter than it was ten years ago.
Which of the following, if true in Verland, most seriously undermines the force of the evidence cited?
题目类型：weaken
受伤的小孩比十年前更多，推出塑料雪橇更危险。。这里有两个假设（1）滑雪小孩的总数保持恒定才能比较受伤率（2）没有除了雪橇材质以外的其他原因。C给出他因，攻击假设2：塑料雪橇让人可以去更广泛的环境下滑雪。引入环境因素可能导致受伤人数上升这一原因，质疑P到C的必然性。
A : 一些孩子仍在用。无关，不能驳倒premise和conclusion之前的联系。
B：很少孩子用防护装置，无关。
C：plastic sleds 用的场合更普遍，因为如果用的普遍，用的次数多了，可能出现事故的频数就多了。正确。
D：发生事故的原因。无关
E：wooden sleds carry more than one，无关。
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