Concept:Interchange the wrongly placed words to form a grammatically correct and meaningful sentence.
Explanation:The original sentence has two errors: "were bolster" and "move to exacerbated".
First, swapping A and C gives "volatile diplomatic relations" and "calculated move", which are correct collocations.
Then, swapping B and D changes "were bolster" to "were exacerbated" and "move to exacerbated" to "move to bolster".
The corrected sentence reads: "The volatile diplomatic relations between the two nations were exacerbated by the calculated move to bolster military presence along the border."
This sentence is both grammatically correct and meaningful.
Therefore, both pairs A-C and B-D must be interchanged.
Answer:A-C and B-D (Option B).