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
#!/usr/bin/env python
# -*- coding: utf-8 -*-

import flask
import redis
import json
import re
from flask import Response, request
import dateutil.parser
import logging

from particle.helpers import *
from particle.common import db

urllib3_logger = logging.getLogger('urllib3')
urllib3_logger.setLevel(logging.CRITICAL)

app = flask.Flask(__name__)

class JSONEncoder(json.JSONEncoder):
  """ This encoder will serialize all entities that have a to_dict
  method by calling that method and serializing the result. """

  def encode(self, obj):
    if hasattr(obj, 'to_dict'):
      obj = obj.to_dict()
    return super(JSONEncoder, self).encode(obj)

  def default(self, obj):

    if hasattr(obj, 'as_dict'):
      return obj.as_dict()

    if isinstance(obj, datetime):
      return obj.isoformat()

    if hasattr(obj, 'to_dict'):
      return obj.to_dict()

    raise TypeError("%r is not JSON serializable" % obj)


def jsonify(obj, status=200, headers=None):
  """ Custom JSONificaton to support obj.to_dict protocol. """
  jsondata = json.dumps(obj, cls=JSONEncoder)

  if 'callback' in request.args:
    jsondata = '%s(%s)' % (request.args.get('callback'), jsondata)

  return Response(jsondata, headers=headers, status=status, mimetype='application/json')

@app.route("/")
def query():

  # parse args
  article_slug = sluggify(request.args.get('url', ''))
  data_sources = request.args.get('data_sources', 'all').split(",")
  start = request.args.get('start', 0)
  end = request.args.get('end', 1e11)
  timestamp = request.args.get('timestamp', None)
  order = request.args.get('order', 'desc')
  include_article = request.args.get('include_article', 'true').lower()
  include_keys = request.args.get('include_keys', 'true').lower()
  
  # pesky boolian problem
  if include_keys=='true':
    include_keys = True
  elif include_keys=='false':
    include_keys = False

  # parse article arg
  if include_article == 'true':
    include_article = True
  elif include_article =='false':
    include_article = False

  # timestamp override
  if timestamp is not None:
    start = timestamp
    end = timestamp

  # fetch data
  results = db.zrangebyscore(article_slug, min = start, max = end)

  # optionally filter out particular datasources
  if data_sources[0] != "all":
    filtered_results = []
    data = [json.loads(r) for r in results]
    for src in data_sources:
      for d in data:
        if d.has_key(src):
          if not include_keys:
            filtered_results.append(json.dumps(d.values()))
          else:
            filtered_results.append(json.dumps(d))
        else:
          for key in d.keys():
            if re.search(src, key):
              if not include_keys:
                filtered_results.append(json.dumps(d.values()))
              else:
                filtered_results.append(json.dumps(d))              

      results = filtered_results

  # optionally order database
  if order=='desc':
    results = [r for r in reversed(results)]
  
  # turn it into a json list
  results = "[%s]" % ",".join(results)

  # create article dict if requested
  if include_article:
    return_pattern = "{\"article\" : %s, \"events\" : %s }"
    article_data = db.get(article_slug+":article")
    
    if article_data is None:
      article_data = "{}"
    
    return return_pattern % (article_data, results)

  # otherwise just return json list
  else: 
    return results

@app.route("/recent-articles/")
def recent():
  
  # parse arg
  limit = request.args.get('limit', 50)

  # just look two days back
  end = current_timestamp()
  start = end - 24*60*60*2
  
  # fetch data
  key = 'article_sorted_set'
  results = db.zrangebyscore(key, min = start, max = end)

  # turn it into a json list
  return "[%s]" % ",".join(results[0:limit+1])

def api(host='0.0.0.0', port=3030, debug=True):
  app.debug = debug
  app.run(host=host, port=port)

```

Which of the following functions or classes contains a `CWE-730: OWASP Top Ten 2004 Category A9 - Denial of Service` vulnerability?

  A) jsonify
  B) recent
  C) api
  D) query
Answer: D