\textbf{115.} The function with the rule $f(x) = (-1)^{[x]}\sin\dfrac{\pi}{2}x$, $x \in \mathbf{Z}$, at integer points, in terms of continuity, is:
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(1) continuous only at even integers \hfill (2) continuous only at odd integers \hfill (3) always discontinuous \hfill (4) always continuous
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