单项选择题 "The error rate is usually higher on the testing set than on the training set." Is it true？（）

单项选择题 Which of these is a reasonable definition of machine learning？（）

单项选择题 Suppose you are working on stock market prediction. You would like to predict whether or not a certain company will win a patent infringement lawsuit (by training on data of companies that had to defend against similar lawsuits). Would you treat this as a classification or a regression problem？（）