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[说明]设有三个关系学生S(学号，姓名，性别，年龄，籍贯)课程C(课程号，课程名，任课老师，所用教材)学生成绩SC(学号，课程号，得分)其中规定各属性定义如下：学号：SNUM 姓名：SNAME 性别：SEX 年龄：AGE 籍贯：NATIVE课程号：CNUM 课程名：CNAME 任课老师：TEACHER 所用教材：BOOK得分：GRADE试用关系代数表达式表示下列查询语句。 [问题2]检索选修全部课程的学生的学号和姓名。

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When people download Sun’s Java program, they can choose to install ______.

A. Open-Office software
B. Google searching Toolbar
C. Microsoft Office
D. Yahoo searching Toolbar

Questions 4 to 7 are based on the following conversation. At the end of the conversation, you will be given 20 seconds to answer the questions. Now listen to the conversation. Why were cars considered the problem in colonial towns

A. Carts scared the pigs away.
B. Carts injured a large number of people.
Carts often moved too slowly.
D. Carts broke down too easily.

[说明] 根据下面所给的AAA数据库，或者按照下列所给的每条SQL查询语句写出相应的功能，或者按照下列所给的每种功能写出相应的SQL查询语句。假设使用名称为AAA的数据库，它包括Students(学号char(8)，姓名varchar(8)，年龄 int，专业varchar(20)，入学日期Date Time)和Score(学号char(8)，课程名varchar(10)，成绩 numeric(5，2))两张表。 [问题4] 请写出一条查询语句，要求显示出Score表中的全部数据，并要求当成绩为空时显示数值-1。

But the developing countries may be impoverished, with populations growing so rapidly that using the land is a means to temporarily avoid worsening poverty and starvation. (Lines 13-15, Para. 1, Passage 3)