调整

app/helpers/exercises_helper.rb

@@ -118,7 +118,7 @@ module ExercisesHelper
         if ex.question_type == Exercise::MULTIPLE  #多选题
           right_user_ids = user_ids
           standard_answer.each do |choice_position|
-            standard_answer_choice_id = ex_choices.select{|ec| ec.choice_position == choice_position}.first.id
+            standard_answer_choice_id = ex_choices.select{|ec| ec.choice_position == choice_position}.first&.id
             right_user_ids = right_user_ids & effictive_users.select{|answer| answer.exercise_choice_id == standard_answer_choice_id}.pluck(:user_id)
           end
           right_users_count = right_user_ids.size
@@ -130,7 +130,7 @@ module ExercisesHelper
           #   end
           # end
         else  #单选题和判断题
-          standard_answer_choice_id = ex_choices.select{|ec| ec.choice_position == standard_answer.first}.first.id
+          standard_answer_choice_id = ex_choices.select{|ec| ec.choice_position == standard_answer.first}.first&.id
           right_users_count = effictive_users.select{|answer| answer.exercise_choice_id == standard_answer_choice_id}.size
         end