input: Write a python function to filter out dictionary entries where the values are not strings.
  assert filterStringDict({'a': 'apple', 'b': 2, 'c': 'carrot'}) == {'a': 'apple', 'c': 'carrot'}
  assert filterStringDict({'x': 'xylophone', 'y': 'yellow', 'z': 3}) == {'x': 'xylophone', 'y': 'yellow'}
  assert filterStringDict({'k1': 1, 'k2': 2, 'k3': 'three'}) == {'k3': 'three'}
output: def filterStringDict(d):
      return {k: v for k, v in d.items() if isinstance(v, str)}