调整

app/controllers/exercises_controller.rb

@@ -137,7 +137,7 @@ class ExercisesController < ApplicationController
         :course_id => @course.id,
         :time => -1,
         :exercise_status => 1,
-        :is_md => params[:md]
+        :is_md => params[:is_md]
       }
       @exercise = Exercise.create!(exercise_options)
     end