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For any integer $\newline$$n$, which of the following are always$\newline$a) two consecutive even numbers?$\newline$b) two consecutive odd numbers?$\newline$$\newline$$n$ and $\newline$$n+2$$\newline$$n-1$ and $\newline$$n+1$$\newline$$2n$ and $\newline$$2n+2$$\newline$$\newline$$2n$ and $\newline$$2n+1$$\newline$$2n-1$ and $\newline$$2n+1$$\newline$$2n+1$ and $\newline$$2n+2$