I think it is when, in the answer choices, 3 choices have something in common while the other 2 choices have something else in common.
So once you identify the 3/2 split, you can decide which is correct similarity.
A) he went yadda yadda yadda
B) he went yadda yadda yadda
C) he had gone yadda yadda yadda
D) he went yadda yadda yadda
E) he had gone yadda yadda yadda
So if you decide "he had gone" is correct, you can eliminate 3 choices right there (A, B, and D). Then you only have C and E left to decide which is the right answer.
Its just a quick way to trim down your answer choices. Maybe somebody else can explain it better but Im sure you get the jist.
And yes, I believe it is only for SC.....but sometimes its hard to spot or not even there.
"George is getting upset!"