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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 item_at_line(root_item, line):

 """
 Find and return the item of the outline explorer under which is located
 the specified 'line' of the editor.
 """

    previous_item = root_item
    item = root_item
    for item in get_item_children(root_item):
        if item.line > line:
            return previous_item
        previous_item = item
    else:
        return item