system: You are an expert security code reviewer. You will be shown a source code file along with a multiple-choice question listing several function or class names from that file. Your task is to identify which one contains the specified CWE vulnerability.

OUTPUT FORMAT: Respond with the single letter of the correct option, wrapped in \boxed{...}. Example: `\boxed{B}`. Output the boxed letter ONLY -- no explanation, no other text.

user: ```python
# Copyright 2022 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,

"""
This application recieves data on HTTP endpoint and inserts into BQ
"""

import json
import logging
import os

from flask import Flask, request, jsonify
from google.api_core import retry
from google.cloud import bigquery
import google.cloud.logging
from google.cloud.logging.handlers import CloudLoggingHandler
from jsonschema import validate, ValidationError


PROJECT_ID = os.getenv('GCP_PROJECT')
BQ_DATASET = os.getenv('BQ_DATASET')
BQ_TABLE = os.getenv('BQ_TABLE')
SERVING_PORT = os.environ.get("SERVING_PORT", 8080)
LOG_LEVEL = os.environ.get("LOG_LEVEL", logging.INFO)
SCHEMA = {
  "type": "object",
  "properties": {
    "Name": { "type": "string" },
    "Age": { "type": "integer" }
  },
  "required": ["Name", "Age"],
  "additionalProperties": False
}

class BigQueryError(Exception):
    '''Exception raised whenever a BigQuery error happened'''

    def __init__(self, errors):
        super().__init__(self._format(errors))
        self.errors = errors

    def _format(self, errors):
        err = []
        for error in errors:
            err.extend(error['errors'])
        return json.dumps(err)


class BQApiClient:
    '''BQ Client to process bq requests'''

    def __init__(self, project_id):
        self._project_id = project_id
        self._client = bigquery.Client(PROJECT_ID)

    def insert(self, data, dataset, table):
        '''Insert data into BQ'''
        LOG.debug("Inserting data  in to %s:%s:%s",
                  PROJECT_ID,  dataset, table)
        table = self._client.dataset(dataset).table(table)
        errors = self._client.insert_rows_json(table,
                                               json_rows=[data],
                                               retry=retry.Retry(deadline=30))
        if errors:
            raise BigQueryError(errors)
        LOG.debug("Successfully Inserted data in to %s:%s:%s",
                  PROJECT_ID,  dataset, table)


def _get_logger():
    client = google.cloud.logging.Client(PROJECT_ID)
    handler = CloudLoggingHandler(client, name="cr-events-processor")
    cloud_logger = logging.getLogger('cr-events-processor')
    cloud_logger.setLevel(LOG_LEVEL)
    cloud_logger.addHandler(handler)
    return cloud_logger


app = Flask(__name__)
LOG = _get_logger()


@app.route("/")
def ping():
    '''Handle ping request'''
    return "BQ insertion Service"


@app.route("/events", methods=['POST'])
def post_events():
    '''Handle event POST request'''
    try:
        event = request.json
        LOG.debug("Recieved event %s", event)
        validate(instance=event, schema=SCHEMA)
        client = BQApiClient(PROJECT_ID)
        client.insert(event, BQ_DATASET, BQ_TABLE)
        return jsonify(status="success"), 200
    except ValidationError as er:
        return jsonify(status="Failure", reason=str(er)), 400
    except BigQueryError as bq_error:
        LOG.error(
            "Failed to insert data in to BQ due to bq_error: %s", str(bq_error))
        return jsonify(status="Failure", reason=str(bq_error)), 500
    except Exception as ex:
        LOG.error(
            "Failed to insert data due to %s", str(ex))
        return jsonify(status="Failure", reason=str(ex)), 500


if __name__ == "__main__":
    app.run(debug=True, host="0.0.0.0", port=int(SERVING_PORT))

```

Which of the following functions or classes contains a `CWE-117: Improper Output Neutralization for Logs` vulnerability?

  A) BigQueryError
  B) post_events
  C) _format
  D) __init__
Answer: B