input: from sklearn.naive_bayes import GaussianNB
  
  def classify_emails(X_train, y_train, X_test):
      """
      Construct a Naive Bayes classifier to classify emails as spam or not spam.
      >>> classify_emails([[0,1], [1,0]], [0,1], [[1,1], [0,0]])
      array([1, 0])
      """
      model = GaussianNB()
      model.fit(X_train, y_train)
      y_pred = model.predict(X_test)
      return y_pred
output:     model = GaussianNB()
      model.fit(X_train, y_train)
      y_pred = model.predict(X_test)
      return y_pred