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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 get_backend_tfvars_file(path, environment, region):
 """Determine Terraform backend file."""

    backend_filenames = gen_backend_tfvars_files(environment, region)
    for name in backend_filenames:
        if os.path.isfile(os.path.join(path, name)):
            return name
    return backend_filenames[-1]