Which syntax turns an existing constraint on?（）

A、ALTER TABLE table_name ENABLE constraint_name;

B、ALTER TABLE table_name STATUS = ENABLE CONSTRAINT constraint _ name;

C、ALTER TABLE table_name ENABLE CONSTRAINT constraint _ name;

D、ALTER TABLE table_name TURN ON CONSTRAINT constraint _ name;

计算机网络信息安全中鉴别交换是在通信进程中，以双方互换约定信息方式确认实体身份机制。（）

A、对

B、错

婴儿服用维生素D预防佝偻病，每日剂量为（）

A、100U

B、400U

C、1000U

D、5000U

E、10000U

二尖瓣轻度狭窄时瓣口面积减至（）

A、1.5cm2以下

B、2.0cm2以下

C、4.0cm2以下

D、4～6cm2

E、6～8cm2

You need to create a table named ORDERS that contains four columns: 1.an ORDER_ID column of number data type 2.a CUSTOMER_ID column of number data type 3.an ORDER_STATUS column that contains a character data type 4.a DATE_ORDERED column to contain the date the order was placed When a row is inserted into the table, if no value is provided for the status of the order, the value PENDING should be used instead. Which statement accomplishes this?（）

A、CREATE TABLE orders ( order_id NUMBER(10), customer_id NUMBER(8), order_status NUMBER(10) DEFAULT 'PENDING', date_ordered DATE );

B、CREATE TABLE orders ( order_id NUMBER(10), customer_id NUMBER(8), order_status VARCHAR2(10) = 'PENDING', date_ordered DATE );

C、CREATE OR REPLACE TABLE orders ( order_id NUMBER(10), customer_id NUMBER(8), order_status VARCHAR2(10) DEFAULT 'PENDING', date_ordered DATE );

D、CREATE OR REPLACE TABLE orders ( order_id NUMBER(10), customer_id NUMBER(8), order_status VARCHAR2(10) = 'PENDING', date_ordered DATE );

E、CREATE TABLE orders ( order_id NUMBER(10), customer_id NUMBER(8), order_status VARCHAR2(10) DEFAULT 'PENDING', date_ordered DATE );

F、CREATE TABLE orders ( order_id NUMBER(10), customer_id NUMBER(8), order_status VARCHAR2(10) DEFAULT 'PENDING', date_ordered VARCHAR2 );

能够支撑价格变动的大额涨幅度是关系营销中的（）。

A、一级关系营销

B、二级关系营销

C、三级关系营销

D、频繁市场营销