Read the code carefully

_MISSING = object()


def merge(base, override=_MISSING):
    if override is _MISSING:
        return f"no override (base={base})"
    if override is None:
        return f"explicit None (base={base})"
    return f"override={override} (base={base})"


print(merge(1))
print(merge(1, None))
print(merge(1, 99))
print(merge(1, _MISSING))

What will the program print? Write here: