O can only go first or fifth. So if F is two spaces before O, then O must be fifth.
(Scroll down for diagrams + explanation)
R can’t be within two spaces of F (rule 2).
This shows that R can’t go anywhere except sixth or seventh. But those are both possible answer choices.
So there must be a further restriction on R. I found it easiest to discover the restriction by trying both possibilities allowed by the first rule: TF and RT.
First, let’s see what happens if we put T before F.
Where can we place S? S can’t go fourth or sixth, because then S would be beside O.
And S can’t go third, because then S would be before P. So S goes seventh, and R goes sixth.
What about if we put T after R, instead?
Then R is still sixth, because 6 and 7 is the only place we can fit TR.
D is CORRECT.
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