(i) if a1, a2, . am are each countable sets, then the union theorem 1.5.8. a1 u a2 uam is countable. (ii) if a is a countable set for each n e n, then uan is countable.

5 i think

explanation:

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answercharacteristics of place include things like economic activity, architecture,and culture,all of which are human elements that alter or can be influenced by the environment;