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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 render_to_string(template_name, context=None, request=None, using=None):
 """ Loads a template and renders it with a context. Returns a string. template_name may be a string or a list of strings. """

    if isinstance(template_name, (list, tuple)):
        template = select_template(template_name, using=using)
    else:
        template = get_template(template_name, using=using)
    return template.render(context, request)