#step1: Guessing number Tornadoes in Nebraska.
We should focus on Tornadoes(Neb) which is black dot line in "Figure Severe Weather Events- 2014":
If we add up the number of Tornadoes in each months, April, about 2 , May about 28 , June about 41, July about 1 , Sep about 1.
2+28 + 41 + 1 + 1 = 73 , of course this is not accurate and confirmed by just eyes, but good point to start.
Please note that this number only includes the numbers of tornadoes which happened from April to October, in other words, the numbers in Jan,Feb,March, Nov, Dec.
We can guess that the numbers of tornadoes in Jan, Feb, March Nov, Dec will not be remarkable, so we can ignore.

#step2 : Calculate EF1 Tornadoes in Nebraska.
If we see "Percentage of Tornadoes by Strength 2014*", EF1 of Nebraska will be about 25%.
So, 73 * 0.25 = 72/4 = 18.125
Please note that this number can be used as minimum number for EF1 Tornadoes in Nebraska.

At this moment, A, C, D, seems to right candidates.

# step3 : Calculate total number of tornadoes which is black solid line in "Figure Severe Weather Events- 2014".
April about 15, May about 50 , June about 85 , July about 8 , August about 10 ,Sep about 8, Oct about 2
= 173.

The number of Tornadoes in N.Dakota and S.Dakota should be less than "Total number of tornadoes" - "The number of tornadoes in nebraska"
173-73 = 100.

# step4 : At most how many EF1 tornadoes could be happened either in N.Dakota or S.Dakota.
Let's focus on possible maximum number of EF1 tornadoes either in N.Dakota or S.Dakota.

The ratio of EF1 in N.Dakota is about 12 %, the ratio in S.Dakota is about 20%.
And, to nail down answers, we do not have to calculate each number of EF1 tornadoes in N.Dakota and S.Dakota, just total of them is important.
For example even we assumed that there are not so many Tornadoes in Kansas, Oklahoma, and most of the EF1 happened S.Dakota except Nebraska.
(The ratio of EF1 in S.Dakota is higher than N.Dakota.)

(173-73) X 0.2 = 20.
This 20 will be maximum sum value of EF1 except Nebraska.

If we see the answers, sum of N.Dakota and S.Dakota D(24=6+18),E(33=13+20),F(99=39+60) are exceeding above 20.
Again, above 20 is maximum sum value and EF1 in N.Dakota and S.Dakota should be less than 20.
(For example, we have some EF1 tornadoes even in Kansas and Oklahoma in figure)

So, D,E,F can NOT be answers.

Based on 2 observations, possible answers when we focus on Nebraska, A,C,D, impossible Answers when we focus on other states except Nebraska, D,E,F,
we can eliminate D from A,C,D, so answer will be A,C.

Answer: A, C