[问答题] 简述面向对象的封装。

现代派诗歌的真正崛起，是在1929年（）的诗集《我的记忆》出版之后。 有机涂装 The EMP table contains these columns: LAST_NAME VARCHAR2 (25) SALARY NUMBER (6,2) DEPARTMENT_ID NUMBER (6) You need to display the employees who have not been assigned to any department. You write the SELECT statement: SELECT LAST_NAME, SALARY, DEPARTMENT_ID FROM EMP WHERE DEPARTMENT_ID = NULL; What is true about this SQL statement ?（） ["The SQL statement displays the desired results.","The column in the WHERE clause should be changed to display the desired results.","The operator in the WHERE clause should be changed to display the desired results.","The WHERE clause should be changed to use an outer join to display the desired results."] 减速起动机中的减速装置可以起到降速增扭的作用。 人道主义概念。 简述面向对象的封装。