Question

Directions: Read the following passage. Fill in each blank with a proper sentence given in the box. Each sentence can be used only once. Note that there are two more sentences than you need.

Most of us would like to have a bright, “white” smile—filled with teeth that would make a Hollywood actor proud. Studies show that up to 52 percent of people are dissatisfied with the color of their teeth. 1. Globally, rows of pearl-white teeth shine out from magazines and cinema screens.

It is hardly surprising, then, that we tend to think that white teeth are not only attractive but also healthy. However, new studies have revealed that pearly teeth don’t always mean great oral health.

2. It can be based on our genes and ages. As you get older, your teeth often become yellower as the enamel（牙釉质）—the hard white outer layer of teeth—begins to wear away. Eating, drinking, smoking and taking certain medications might also discolor your teeth. These stains don’t actually indicate a problem with dental health. You can have pearl-white teeth and still have cavities（龋齿的洞）. Likewise, you can have perfectly healthy teeth that are yellowish or even brownish. 3.

There is even one type of stain that some researchers believe might protect against tooth decay. This is the “black stain” which you sometimes see along teeth at the edges of the gum line（牙龈线）. It can look like a series of dark dots. While the cause of the black stain has been in debate for more than a century, some studies have found that children with the stain are less likely to have tooth decay. It’s thought that some microbes in the stain might be somehow protective.

So what if you still want pearl-white teeth, regardless of what they say about your health? There is a wide range of products you can use. Some kinds of toothpaste promise a whitening effect. Most of them contain substances that rub stains off your teeth. Others add some blueish substances to your yellowish teeth, resulting in a bright white color. 4.

Of course, unless you continue using the product or receiving the whitening treatment, the whiteness will only last for as long as you avoid the foods and drinks that cause the stains in the first place. But now you know that even without that Hollywood white smile, it doesn’t mean you don’t have healthy teeth.

A.Many of the experiments on tooth color have been conducted in laboratory test tubes, rather than in the mouths of living people.

B.In countries such as the United States, tooth whitening is one of the most commonly requested dental treatments.

C.The color of our teeth is influenced by a number of factors.

D.It is no surprise that the red wine leaves the strongest stains.

AB. There are also professional whitening treatments, but whitening can cause temporary sensitivity in some people’s teeth or gums.

AC. Of course, in some cases, discoloration can indicate decay or other diseases, so it is worth getting stains checked out by a dentist.

Answer

1.B

2.C

3.AC

4.AB

【解析】

本文是一篇说明文，介绍了影响牙齿的颜色的几个因素以及牙齿不白并不代表你的口腔不健康。

1.空前说表明，高达52%的人对牙齿的颜色不满意，此处举例证明人们对牙齿的颜色不满意，

故B项（在美国等国家，牙齿美白是最常见的牙科治疗要求之一）符合语境。故选B。

2.空后从基因、年龄、吃、喝、吸烟和服用药物等几个方面介绍了对牙齿的颜色的影响，此处是主题句，讲的是影响牙齿的颜色的因素有很多，故C项（我们牙齿的颜色受许多因素的影响）符合语境，故选C。

3.空前说同样的，你也可以拥有完全健康的黄牙，甚至是棕色的，这说明不是白色并不代表你的牙齿不健康，接下来此处讲的是不正常的变色情况，故AC项（当然，在某些情况下，变色可能意味着腐烂或其他疾病，所以让牙医检查污渍是值得的）符合语境。故选AC。

4.空前说有些牙膏有美白的功效，它们中的大多数含有能擦掉牙齿上污渍的物质，另一些则是在淡黄的牙齿上添加一些蓝色物质，从而产生亮白色，此处接着介绍另外一种美白牙齿的方法，故AB项（也有专业的美白治疗，但美白会导致一些人的牙齿或牙龈暂时敏感）符合语境。故选AB。