I am trying to programmatically create a question on mechanical turk using boto3, but I seem to be doing something wrong, since the `ExternalQuestion` data structure that is required for `create_hit` seems to be missing. 

I try to create the HIT like so:

```
import boto3

#...

client = boto3.client(
    'mturk',
    endpoint_url=endpoint_url,
    region_name=region_name,
    aws_access_key_id=aws_access_key_id,
    aws_secret_access_key=aws_secret_access_key,
)

question = ExternalQuestion(external_url=question_target, frame_height=800)

response = client.create_hit(
        MaxAssignments=10,
        Title='Test',
        Description='This is a test of ExternalQuestion',
        Question=question,
        AssignmentDurationInSeconds=60,
        LifetimeInSeconds=24 * 60 * 60,
        Reward=0.01)

```

Which fails:

```
Traceback (most recent call last):
  File "createTask.py", line 21, in <module>
    question = ExternalQuestion(external_url=question_target, frame_height=800)
NameError: name 'ExternalQuestion' is not defined

```

Any advice on how to proceed is highly appreciated.