Examine the following command: CREATE TABLE (prod_id number(4), Prod_name varchar2 (20), Category_id number(30), Quantity_on_hand number (3) INVISIBLE); Which three statements are true about using an invisible column in the PRODUCTS table?（） The %ROWTYPE attribute declarations in PL/SQL to access a row will not display the invisible column in the output.。 The DESCRIBE commands in SQL *Plus will not display the invisible column in the output.。 Referential integrity constraint cannot be set on the invisible column.。 The invisible column cannot be made visible and can only be marked as unused.。 A primary key constraint can be added on the invisible column.。
《包氏父子》逼真地描绘了可悲的父亲老包和可笑的儿子小包，而且还通过这对父子的矛盾，表现了社会的变化，是（）小说创作的代表作之一。
粗糙表面的接触
溶解乙炔气瓶：瓶内（），用于充装乙炔的气瓶。 装有多孔填料及溶剂。 什么也没有。 实心。
The database instance is currently using SPFILE. View the Exhibit and examine the error that youreceived while running the DB Structure Integrity check. Given below are the steps to recover from the error in random order: 1: Shut down the instance, if not already done. 2: Copy one of the remaining control files to a new location. 3: Change the value of the CONTROL_FILES initialization parameter to correspond to the new location of the control files. 4: Start up the database instance to the NOMOUNT stage. 5: Recover the database to the point of failure of the control file. 6: Open the database. Identify the correct sequence of steps() 1，2，4，3，5，6。 2，4，3，5，6；1 not required。 4，5，6，2，3；1 not required。 5，2，3，4；1 and 6 not required。
地网接地体之间的连接，应采用电焊或气焊连接，不宜采用螺钉连接或铆接；无法使用电焊或氧焊的，建议使用（）焊接。
