Update MLVU answer parsing (EvolvingLMMs-Lab#364)

lmms_eval/tasks/mlvu/utils.py

@@ -51,12 +51,24 @@ def mlvu_doc_to_text(doc, lmms_eval_specific_kwargs=None):
 
 def extract_characters_regex(s):
     s = s.strip()
-    if ")" in s:
-        index = s.index(")")
-        pred = s[index - 1 : index]
-        return pred
-    else:
-        return s
+    answer_prefixes = [
+        "The best answer is",
+        "The correct answer is",
+        "The answer is",
+        "The answer",
+        "The best option is" "The correct option is",
+        "Best answer:" "Best option:",
+    ]
+    for answer_prefix in answer_prefixes:
+        s = s.replace(answer_prefix, "")
+
+    if len(s.split()) > 10 and not re.search("[ABCD]", s):
+        return ""
+
+    matches = re.search(r"[ABCD]", s)
+    if matches is None:
+        return ""
+    return matches[0]
 
 
 def mlvu_process_results(doc, results):