Explanation

The sentence contrasts the rules of etiquette with the detailed written regulations regarding play, so you need something like vague or unwritten for the blank. Both express and manifest are nearly the opposite of what you’re looking for, so eliminate choices (C) and (F).

Be careful about laconic: It means using few words, but not unspoken, so eliminate choice (B).

Reclusive, which means withdrawn from society, doesn’t make sense in the blank, so eliminate choice (E). Both implicit and tacit can mean unwritten, so choices (A) and (D) give you appropriate, equivalent sentences.

Hence options A and D is correct!

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