The 7-choose-5 section gives you five gaps in a passage and seven candidate sentences. Two of those seven are distractors that will not fit anywhere.
Read the whole passage first without looking at the candidates. Get the argument.
Now look at each gap. What comes before it? What comes after it? Underline the pronouns and connectives near each gap — 'this', 'however', 'in addition' — these are the seams the correct candidate has to fit.
Match candidates to gaps by these seams, not by topic. Two sentences might be about the same topic but only one will grammatically join what comes before and after.
Do the easiest gaps first. The last gap you fill in should be the hardest one, and by then you have only two candidates left to choose between.