old_contents: module.exports = function(mongoose) {
      var studentSchema = new mongoose.Schema({
          question: String,
          tier: Number,
          tags: [String]
      });
  
      return mongoose.model('Student', studentSchema);
  };
  
new_contents: module.exports = function(mongoose) {
      var questionSchema = new mongoose.Schema({
          question: String,
          tier: Number,
          tags: [String]
      });
  
      return mongoose.model('Question', questionSchema);
  };
  
subject: Fix model name.