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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def label_subplot(ax=None, x=0.5, y=-0.25, text="(a)", **kwargs):
 """Create a subplot label."""

    if ax is None:
        ax = plt.gca()
    ax.text(x=x, y=y, s=text, transform=ax.transAxes,
            horizontalalignment="center", verticalalignment="top", **kwargs)