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
import requests
from flask import Flask, request, redirect, url_for
from src.classifier import MyTextClassifier
from werkzeug.utils import secure_filename
import os
import json

APP_ROOT = os.path.dirname(os.path.abspath(__file__))
UPLOAD_FOLDER = APP_ROOT + "/src/chats"

app = Flask(__name__)
app.config['UPLOAD_FOLDER'] = UPLOAD_FOLDER
#clf = None

clfdict = {}


@app.route('/hi/<name>')
def say_hi(name):
    return 'Hello, %s!' % name


@app.route('/findauthor/<text>/')
def findauthor(text):
    print([text])
    return clf.predictAuthor([text])[0]


# When using Postman:
# POST to https://fb-text-classifier.herokuapp.com/upload/
# Body: form-data
# Key - value:
#   size (Text) - original
#   file (File) - "Choose Files"
@app.route('/upload/', methods=['POST'])
def upload_file():
    if request.method == 'POST':
        # check if the post request has the file

        if 'file' not in request.files:
            return "No file selected"

        file = request.files['file']

        # if user does not select file, browser also
        # submit a empty part without filename
        if file.filename == '':
            return "No file selected"

        if file:
            filename = secure_filename(file.filename)
            path = os.path.join(app.config['UPLOAD_FOLDER'], filename)
            file.save(path)
            global clf
            clf = MyTextClassifier(path)
            return "File upload success"
    return "Done"


# https://github.com/hartleybrody/fb-messenger-bot
@app.route('/', methods=['GET'])
def verify():
    # when the endpoint is registered as a webhook, it must echo back
    # the 'hub.challenge' value it receives in the query arguments
    if request.args.get("hub.mode") == "subscribe" and request.args.get("hub.challenge"):
        if not request.args.get("hub.verify_token") == os.environ["VERIFY_TOKEN"]:
            return "Verification token mismatch", 403
        return request.args["hub.challenge"], 200

    return "<h1>Hello, this is fb-text-classifier.</h1>\n<p>Made by Siim Raudsepp and Kristjan Puusepp</p>", 200


@app.route('/', methods=['POST'])
def webhook():
    global clfdict
    # endpoint for processing incoming messaging events
    data = request.get_json()
    print(data)
    if data["object"] == "page":

        for entry in data["entry"]:
            for messaging_event in entry["messaging"]:
                if messaging_event.get("read"):
                    pass
                else:
                    try:
                        if messaging_event.get("message"):  # someone sent us a message

                            sender_id = messaging_event["sender"]["id"]        # the facebook ID of the person sending you the message
                            print("sender_id: " + sender_id)

                            try:
                                for i in messaging_event["message"]["attachments"]:
                                    print("Checking if message contains a file...")
                                    if i["type"] == "file":
                                        print("User sent a file. Downloading it...")
                                        r = requests.get(i["payload"]["url"])
                                        send_message(sender_id, "Clearing old classifier...")
                                        clfdict[sender_id] = None
                                        dumpclean(clfdict)
                                        send_message(sender_id, "Learning from the file...")

                                        clfdict[sender_id] = MyTextClassifier(r.content)

                                        print("saved to dictionary at [" + sender_id + "]")
                                        send_message(sender_id, "Learning finished.")
                                        break
                                    else:
                                        print("Not a file")
                                        break
                            except Exception:
                                print("Something went wrong, could not download the file")

                            recipient_id = messaging_event["recipient"]["id"]  # the recipient's ID, which should be your page's facebook ID
                            message_text = messaging_event["message"]["text"]  # the message's text

                            clf = None
                            try:
                                clf = clfdict[sender_id]
                                print("Got classifier with id " + sender_id)
                            except Exception:
                                print("cannot get your classifier " + sender_id)
                            if clf:
                                send_message(sender_id, clf.predictAuthor([message_text])[0] + " is the author of that text.")
                            else:
                                noclassifier = "You have not uploaded your chat history yet. Please rename the .html file to .txt and attach it to this chat."
                                send_message(sender_id, noclassifier)

                        if messaging_event.get("delivery"):  # delivery confirmation
                            pass

                        if messaging_event.get("optin"):  # optin confirmation
                            pass

                        if messaging_event.get("postback"):  # user clicked/tapped "postback" button in earlier message
                            pass

                    except KeyError:
                        return "oops", 200

    print("sending response: ok, 200")
    return "ok", 200


def dumpclean(obj):
    if type(obj) == dict:
        for k, v in obj.items():
            if hasattr(v, '__iter__'):
                print(k)
                dumpclean(v)
            else:
                print('%s : %s' % (k, v))
    elif type(obj) == list:
        for v in obj:
            if hasattr(v, '__iter__'):
                dumpclean(v)
            else:
                print(v)
    else:
        print(obj)


def send_message(recipient_id, message_text):

    print("sending message to {recipient}: {text}".format(recipient=recipient_id, text=message_text))

    params = {
        "access_token": os.environ["PAGE_ACCESS_TOKEN"]
    }
    headers = {
        "Content-Type": "application/json"
    }
    data = json.dumps({
        "recipient": {
            "id": recipient_id
        },
        "message": {
            "text": message_text
        }
    })
    r = requests.post("https://graph.facebook.com/v2.6/me/messages", params=params, headers=headers, data=data)
    if r.status_code != 200:
        print(r.status_code)


if __name__ == "__main__":
    port = int(os.environ.get("PORT", 5000))
    app.run(port=port, debug=True, threaded=True)


```

Which of the following functions or classes contains a `CWE-918: Server-Side Request Forgery (SSRF)` vulnerability?

  A) say_hi
  B) verify
  C) upload_file
  D) webhook
Answer: D