The number of large and medium sized tornadoes reported annually has remained roughly constant
Why this is right
We know that twice as many tornadoes per year are reported now vs. in 1950. Let's say for example, 1950 - 100 tornadoes reported per year 2020 - 200 tornadoes reported per year This answer is saying that the number of Large/Medium tornadoes reported has not gone up. Let's pretend it's 90 in both cases. 1950 Now Large/Med 90 90 Small Total 100 200 So, by subtraction, that tells us how many Small tornadoes were detected in each time period. 1950 Now Large/Med 90 90 Small 10 110 Total 100 200 It, of course, doesn't matter what numbers we use (or that we use numbers at all). The point of the answer choice is "All of the increase in reported tornadoes comes from smaller tornadoes". If we're reporting twice as many tornadoes, and the increase is purely due to an uptick in smaller tornadoes, that boosts the plausibility of the author's hypothesis that what has really changed is our improved tornado-finding abilities. With primitive tornado-finding abilities, we would be able to detect Large / Medium pretty easily, but we would struggle to detect the Smaller ones. With improved tornado-finding abilities, we would now be able to detect more Smaller ones. So this is a piece of information that helps corroborate our author's storyline.
Skill tested: Strengthen · how this choice captures the argument's function is the move to repeat next time.