input: Write a function to parse a JSON data structure and return the name, age, and occupation fields. The function should accept a JSON string as input and return a tuple containing the name, age, and occupation. If the input is not a valid JSON string, the function should return an error message.
  assert parse_json('{"name": "John", "age": 18, "occupation": "Software Engineer"}')==('John', 18, 'Software Engineer')
  assert parse_json('{"name": "Alice", "age": 22, "occupation": "Teacher"}')==('Alice', 22, 'Teacher')
  assert parse_json('{"name": "Bob", "age": 35, "occupation": "Doctor"}')==('Bob', 35, 'Doctor')
  assert parse_json('{"name": "Eve", "age": 28, "occupation": "Engineer"}')==('Eve', 28, 'Engineer')
  assert parse_json('{"name": "Charlie", "age": 40, "occupation": "Lawyer"}')==('Charlie', 40, 'Lawyer')
output: try:
      data = json.loads(json_string)
      return (data['name'], data['age'], data['occupation'])
  except (json.JSONDecodeError, KeyError):
      return "Error: Invalid JSON string"