You should always question an argument that turns a quantitative metric such as "greater number of injuries" into a qualitative metric such as "less safe."

We're given that a greater NUMBER of children have been injured while sledding than were 10 years ago. Does that have to mean that their sleds are less safe? We should ask:
- Are there more children sledding now than there were 10 years ago?
- Are children sledding more often?
- Is the severity of accidents the same? Safety isn't just defined by number of accidents, but how severe they are.
- Is the difference in sleds the cause of the change, or is there some other behavioral difference in children over 10 years?

If we want to WEAKEN the argument, we need a reason to suggest that number of accidents does not correlate to safety.

(A) A few children still use traditional wooden sleds.
This would strengthen the argument - it's more likely that the injuries were due to the plastic sleds.

(B) Very few children wear any kind of protective gear, such as helmets, while sledding.
Again, this would strengthen - differences in injuries is more likely to be due to the sleds, not protective gear.

(C) Plastic sleds can be used in a much wider variety of snow conditions than wooden sleds can.
Correct! This indicates that children are likely to sled more often. More sledding = more time spent / opportunity for injuries, without implying that the sled is to blame.

(D) Most sledding injuries occur when a sled collides with a tree, a rock, or another sled.
This would be true of wooden and plastic sleds, so it wouldn't help us compare.

(E) Because the traditional wooden sleds can carry more than one rider, an accident involving a wooden sled can result in several children being injured.
Since the metric we're given is "number of children injured," this wouldn't make a difference. If the sled injures one person or multiple people at a time, it could still be judged unsafe.

The answer is C.