diff --git a/app/account_service.py b/app/account_service.py
index a7ed0c4..e079514 100644
--- a/app/account_service.py
+++ b/app/account_service.py
@@ -1,6 +1,7 @@
 from flask import *
-from Login import check_username_availability, verify_user, add_user, get_expiry_date, change_password, WarningMessage
-
+from flask import escape, redirect
+from Login import (WarningMessage, add_user, change_password,
+                   check_username_availability, get_expiry_date, verify_user)
 
 # 初始化蓝图
 accountService = Blueprint("accountService", __name__)
diff --git a/app/model/article.py b/app/model/article.py
index a3b4bf7..517a856 100644
--- a/app/model/article.py
+++ b/app/model/article.py
@@ -1,6 +1,8 @@
-from model import *
 from datetime import datetime
 
+from model import *
+
+
 def add_article(content, source="manual_input", level="5", question="No question"):
     with db_session:
         # add one article to sqlite
@@ -32,3 +34,15 @@ def get_page_articles(num, size):
             x
             for x in Article.select().order_by(desc(Article.article_id)).page(num, size)
         ]
+
+def get_article_by_id(article_id):
+    article_id &= 0xFFFFFFFF  # max 32 bits
+    with db_session:
+        article = Article.select(article_id=article_id).first()
+        if article:
+            return article.to_dict()
+
+
+def get_all_articles():
+    with db_session:
+        return [art.to_dict() for art in Article.select()[:]]
\ No newline at end of file
diff --git a/app/test/test_vocabulary.py b/app/test/test_vocabulary.py
new file mode 100644
index 0000000..9b09b3e
--- /dev/null
+++ b/app/test/test_vocabulary.py
@@ -0,0 +1,36 @@
+import math
+
+from vocabulary import ArticleVocabularyLevel, UserVocabularyLevel
+
+
+def test_article_level():
+    ''' Boundary case test '''
+    article = ArticleVocabularyLevel('')
+    assert article.level == 0
+    
+def test_user_level():
+    ''' Boundary case test '''
+    user = UserVocabularyLevel({})
+    assert user.level == 0
+    
+def test_article_level_3():
+    ''' Normal case test '''
+    article = ArticleVocabularyLevel('This is an interesting article that frequently uses the word "banana".')
+    assert article.level == 3.090909090909091
+    
+def test_user_level_4():
+    ''' Normal case test '''
+    d = {'apple': ['BBC', 'CTE4'], 'banana': ['BBC', 'CTE4']}
+    user = UserVocabularyLevel(d)
+    assert user.level == 4.0
+    
+def test_article_level_5():
+    ''' Abnormal case test '''
+    article = ArticleVocabularyLevel('This is an interesting article that frequently uses the word "banana".')
+    assert article.level != 5.0
+    
+def test_user_level_6():
+    ''' Abnormal case test '''
+    d = {'apple': ['BBC', 'CTE4'], 'banana': ['BBC', 'CTE4']}
+    user = UserVocabularyLevel(d)
+    assert user.level != 6.0
\ No newline at end of file
diff --git a/app/vocabulary.py b/app/vocabulary.py
new file mode 100644
index 0000000..37e7dcb
--- /dev/null
+++ b/app/vocabulary.py
@@ -0,0 +1,52 @@
+import pickle
+
+
+def load_record(pickle_fname):
+    with open(pickle_fname, 'rb') as f:
+        d = pickle.load(f)
+    return d
+
+
+class VocabularyLevelEstimator:
+    _test = load_record('static/words_and_tests.p')  # map a word to the sources where it appears
+
+    @property
+    def level(self):
+        if self.word_lst == []:
+            return 0
+        total = 0.0  # TODO: need to compute this number
+        num = 0
+        for word in self.word_lst:
+            num += 1
+            if word in self._test:
+                total += len(self._test[word])
+                print(f'{word} : {self._test[word]}')
+            else:
+                print(f'{word}')
+        return total / num
+
+
+class UserVocabularyLevel(VocabularyLevelEstimator):
+    def __init__(self, d):
+        self.d = d
+        self.word_lst = list(d.keys())
+        # just look at the most recently-added words
+
+
+class ArticleVocabularyLevel(VocabularyLevelEstimator):
+    def __init__(self, content):
+        self.content = content
+        self.word_lst = content.lower().split()
+        # select the 10 most difficult words
+
+    def top_ten_difficult_words(self):
+        pass
+
+
+if __name__ == '__main__':
+    d = load_record('frequency_arnold.pickle')
+    # print(d)
+    user = UserVocabularyLevel(d)
+    print(user.level)  # level is a property
+    article = ArticleVocabularyLevel('This is an interesting article that frequently uses the word "banana".')
+    print(article.level)