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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_bel_versions() -> List[str]: """Get BEL Language versions supported Get the list of all BEL Language versions supported. The file this depends on is generated by belspec_yaml2json and is kept up to date using `make update_ebnf` or `make update_parsers`. You can also run `belspec_yaml2json` directly as it's added as a command by pip install. Returns: List[str]: list of versions """


    spec_dir = config["bel"]["lang"]["specifications"]

    fn = f"{spec_dir}/versions.json"
    with open(fn, "r") as f:
        versions = json.load(f)

    return versions