问题 选择题

只用1,2,3三个数字组成一个四位数,规定这三个数必须同时使用,且同一数字不能相邻出现,这样的四位数有(    )

A.6个

B.9个

C.18个

D.36个

答案

答案:C

题目分析:先在1,2,3中选一个数作为重复用的数有3种不同选法,再将其与两个数排成一排有,因要求重复使用的数不相邻,故用插空法,在排成一排的两个数形成的三个空挡中任取两个空挡将重复使用的两个数放进去有种不同的的方法,根据分步计数原理,共有不同排法为3=18,一种排法对应一个满足条件的四位数,故这样的四位数由18个,故选C.

选择题
阅读理解

“In only six days I lost seven pounds of weight.”

“Two full inches in the first three days!”

These are the kinds of statements used in magazine,newspaper,radio and television ads,promising new shapes and new looks to those who buy the medicine or the device. The promoters of products say they can shape the legs,slim the face,smooth wrinkles,or in some other way to add to beauty or desirability.

Often such products are nothing more than money­making things for their promoters. The results they produce are questionable,and some are dangerous to health.

To understand how these products can be legally promoted to the public,it is necessary to understand something of the laws covering their regulation. If the product is a drug,FDA(Food and Drug Administration)can require proof under the Food,Drug,and Cosmetic Act that is safe and effective before it is put on the market. But if the product is a device,FDA has no authority to require the proof of safety or effectiveness. If a product already on the market is a danger to health,FDA can request the producer or distributor to remove it from the market voluntarily,or it can take legal action,including seizure (查封) of the product.

One notable case a few years ago involved an electrical device called the Relaxacisor,which had been sold for reducing the waistline. The Relaxacisor produced electrical shocks to the body through contact pads. FDA took legal action against the distributor to stop the sale of the device on the grounds that it was dangerous to health and life.

Obviously,most of the devices on the market have never been the subject of court proceedings (法律诉讼),and new devices appear continually. Before buying,it is up to the consumer to judge the safety or effectiveness of such items.

小题1:It can be inferred that the ads mentioned in the text are________.

A.objective

B.costly

C.unreliable

D.illegal小题2:Which of the following is TRUE according to the text?

A.The court is in charge of removing dangerous products.

B.New products are more likely to be questionable. 

C.The production of a device must be approved by FDA.

D.The promoters usually just care about profits.

小题3:FDA can ask for the proof of safety and effectiveness of a product________.

A.if it is a drug

B.if it is a device

C.if its consumers make complaints

D.if its distributors challenge FDA's authority小题4:The Relaxacisor is mentioned as________.

A.a product which was designed to produce electricity

B.a product whose distributor was involved in a legal case

C.a successful advertisement of a beauty product

D.an example of a quality beauty product