def METHOD_NAME(course_key_str, block, user_id):
    """
    Return submissions for `block`.
    """
    # Load the actual student submissions for `block`.
    # Note this requires one giant query that retrieves all student submissions for `block` at once.
    block_id = str(block.scope_ids.usage_id.replace(branch=None, version_guid=None))
    block_type = _get_type(block)
    if block_type == 'pb-answer':
        block_id = block.name  # item_id of Long Answer submission matches question ID and not block ID
    if not user_id:
        return sub_api.get_all_submissions(course_key_str, block_id, block_type)
    else:
        student_dict = {
            'student_id': user_id,
            'item_id': block_id,
            'course_id': course_key_str,
            'item_type': block_type,
        }
        return sub_api.get_submissions(student_dict, limit=1)