from typing import Dict


def largest_valued_key(dic: Dict[str, set]) -> str:
    """Find the key with the largest value."""
    biggest_size = -1
    biggest_key = None
    for key, value in dic.items():
        length = len(value)
        if length > biggest_size:
            biggest_size = length
            biggest_key = key
    assert isinstance(biggest_key, str)
    return biggest_key