Okay, so this is a cannot be true question; or if you'd prefer, a must be false question.
The best way, in my opinion, to attack these questions is to briefly become familiar with the stimulus, and THEN move to the answer choices, knocking answer choices out that could be true.
(A) This answer choice is the trickiest one of the bunch. It states that the number of ski injuries that occurred on the slopes was greater in 1980 than in 1950. You might be thinking, "okay, in 1950, there were 9 accidents per 1000 people, and in 1980 there were 3 accidents per 1000 people. So it cannot be true that there were more accidents in 1980 than there were in 1950."
However, this reasoning is faulty because you don't know exactly how many skiers there were in either scenario (1950 & 1980).
For instance, if there were 1000 skiers in 1950, then only 9 were hurt. If there were 5000 skiers in 1980, then 15 were hurt.
Can you see now, through my illustration, how more people could have been hurt in 1980? If so, then you understand the logic behind why this answer choice could be true, and thus, an incorrect answer choice.
(C) is wrong because this answer could be true. There is nothing in the stimulus that talks about the reporting of ski injuries, and thus, we cannot infer anything about it - cross it out.
(D) is wrong because we don't know anything about the total number of skiers from 1950 to 1980, thus, this answer could be true - cross it out.
(E) Okay, this answer choice talks about ski injuries occurring 1980 that happened to people who were not skiing, and we are told nothing about these types of injuries in the stimulus. Thus, this answer choice could be true - cross it out.
Answer choice (B), our correct answer choice. This is the correct answer choice because it cannot be true (it must be false). The stimulus gives us the odds of being injured for both 1950 and 1980, which is 9/1000 and 3/1000, respectively. What that means is that the odds (the likelihood of being injured) are less in 1980 than they are in 1950, which is the exact opposite of what this answer choice says. Therefore, answer choice (B) must be false and is your correct answer.
Happy studying!