问题 单项选择题

设有学生表:STUD(学号,姓名,性别,年龄,专业),把学号为“20030019”的学生从该表中删除掉的语句是______。

A.DELETE STUD WHERE 学号=“20030019”

B.DELETE FROM STUDWHERE学号=“20030019”

C.DELETE TABLE STUD WHERE学号=“20030019”

D.DELETE FROM WHERE 学号=“20030019”

答案

参考答案:B

解析: 删除语句的一般格式为:DELETE FROM表名[WHERE<条件>]。该语句的功能是在指定的表中删除满足条件的那些记录。当没有使用WHERE子句时,则删除表中的全部记录。选项A、C、D的语句均不符合语法格式。

阅读理解

However wealthy we may be, we can never find enough hours in the day to do everything we want. Economics deals with this problem through the concept of opportunity cost, which simply refers to whether someone’s time or money could be better spent on something else.

Every hour of our time has a value. For every hour we work at one job we could quite easily be doing another, or be sleeping or watching a film. Each of these options has a different opportunity cost—namely, what they cost us in missed opportunities.

Say you intend to watch a football match but the tickets are expensive and it will take you a couple of hours to get to and from the stadium. Why not, you might reason, watch the game from home and use the leftover money and time to have dinner with friends? This—the alternative use of your cash and time—is the opportunity cost.

For economists, every decision is made by knowledge of what one must forgo—in terms of money and enjoyment—in order to take it up. By knowing precisely what you are receiving and what you are missing out on, you ought to be able to make better-informed, more reasonable decisions. Consider that most famous economic rule of all: there’s no such thing as a free lunch. Even if someone offers to take you out to lunch for free, the time you will spend in the restaurant still costs you something in terms of forgone opportunities.

Some people find the idea of opportunity cost extremely discouraging: imagine spending your entire life calculating whether your time would be better spent elsewhere doing something more profitable or enjoyable. Yet, in a sense it’s human nature to do precisely that—we assess the advantages and disadvantages of decisions all the time.

In the business world, a popular phrase is “value for money.” People want their cash to go as far as possible. However, another is fast obtaining an advantage: “value for time.” The biggest restriction on our resources is the number of hours we can devote to something, so we look to maximize the return we get on our investment of time. By reading this passage you are giving over a bit of your time which could be spent doing other activities, such as sleeping and eating. In return, however, this passage will help you to think like an economist, closely considering the opportunity cost of each of your decisions.

小题1:According to the passage, the concept of “opportunity cost” is applied to ________.

A.making more money

B.taking more opportunities

C.reducing missed opportunities

D.weighing the choice of opportunities小题2:The “leftover ... time” in Paragraph 3 probably refers to the time ________.

A.spared for watching the match at home

B.taken to have dinner with friends

C.spent on the way to and from the match

D.saved from not going to watch the match小题3:What are forgone opportunities?

A.Opportunities you forget in decision-making.

B.Opportunities you give up for better ones.

C.Opportunities you miss accidentally.

D.Opportunities you make up for.

单项选择题