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已知集合 $M=\{x \mid-4 < x \leqslant 1\}, N=\{x \mid-1 < x < 3\}$, 则 $M \cup N=$
A. $\{x \mid-4 < x < 3\}$     B. $\{x \mid-1 < x \leq 1\}$     C. $\{0,1,2\}$     D. $\{x \mid-1 < x < 4\}$         
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