diff --git a/app/difficulty.py b/app/difficulty.py
index 50aa179..f79ca35 100644
--- a/app/difficulty.py
+++ b/app/difficulty.py
@@ -75,12 +75,37 @@ def revert_dict(d):
     return d2
 
 
+def combine_words_through_grammar(lst,d): #通过语法合并同一单词的不同形式
+    lst1=lst
+    for index,word in enumerate(lst):
+        change_word=''
+        if word.endswith('ies'):      #语法条件匹配
+            change_word=word[:-3]+'y'
+        elif word.endswith('es'):
+            change_word=word[:-2]
+        elif word.endswith('s'):
+            change_word=word[:-1]
+        elif word.endswith('ed'):
+            change_word=word[:-2]
+        elif word.endswith('en'):
+            change_word=word[:-2] + 'an'
+        else:
+            pass
+        for word2 in d:
+            if change_word==word2:
+                lst1[index]=change_word
+                break
+    return lst1   
+
 def user_difficulty_level(d_user, d):
     d_user2 = revert_dict(d_user) # key is date, and value is a list of words added in that date
     count = 0
     geometric = 1
     for date in sorted(d_user2.keys(), reverse=True): # most recently added words are more important while determining user's level
         lst = d_user2[date] # a list of words
+        #print(lst)
+        lst=combine_words_through_grammar(lst,d) #合并单词的不同形式
+        #print(lst)
         lst2 = [] # a list of tuples, (word, difficulty level)
         for  word in lst:
             if word in d: