Open the brackets using an appropriate Tense form of the verbs. Discuss cases where different variants are possible.
Mrs Hay (drive) along a small country road when she (see) a man at the side of the road. He (wave) and (point) at his car. Mrs Hay (stop) and (ask) the man if he (be) all right. “My car is broken”, said the man. “Where you (want) to go?” asked Mrs Hay. “London”, replied the man. “Well, I (not go) to London, but I (give) you a lift to the station, if you like.” On the way to the station they chatted. “ You (work) in London?” asked Mrs Hay. “No, I don’t. I (run) my own business in Oxford. But today I (have) lunch with a friend in London – we always (have) lunch together on Fridays. I (promise) to meet her at one o’clock”. “There (be) a train at 11.30. I don’t think you (be) late for your appointment.” When they (arrive) at the station, a train (stand) at the platform. “That’s your train,” said Mrs Hay, - “You (catch) it if you’re quick”. After the man (get out) of the car, Mrs Hay (drive away). A few minutes later she (realize) that she (make) a mistake: it was the wrong train. She went back to the station, but the train wasn’t there: it (leave) already. Mrs Hay asked at the information desk where the train (go). “It’s the express to Edinburgh and it (not stop),” the information clerk told her.
Summary
Text I. The influence of xylitol
Chewing gum containing xylitol, a sweetener with antimicrobial properties, temporarily suppresses bacteria that cause tooth decay, according to university of Minnesota researchers.
In the experiment, the gum was chewed after treatment with an antimicrobial mouthrinse and chlorhedixine. The mouthrinse is used to reduce the bacteria (mutans streptococci) linked to increased risk of tooth decay. However, without further intervention the bacteria tend to return to pre-treatment levels. This study demonstrated that xylitol chewing gum can be used to extend the suppression of mutans streptococci.
In the study supported by a National Institutes of Health, National Institute of Dental and Craniofacial Research grant, the authors evaluated the effect of xylitol chewing gum on bacteria re-growth. Procter & Gamble supplied a portion of the mouthrinse used in the study.
The authors selected 151 subjects with elevated mutans streptococci levels. The subjects rinsed with chlorhexidine gluconate mouthrinse twice daily for two weeks and were randomly assigned to a test, placebo or control group. In the test group 51 persons chewed xylitol gum three times daily after meals for a minimum of 5 minutes each time. The placebo group of 50 people chewed a commercial sorbitol-aspartame and saccharin-sweetened chewing gum three times daily after meals for a minimum of five minutes. The control group of 50 did not chew any gum. The study lasted three months.
"Use of xylitol chewing gum can retard return of oral bacteria after chlorhexidine treatment." the author concluded after the three-month period. "Used in conjunction with other caries control strategies, such diet modification, fluoride and sealants, a xylitol-sweetened chewing gum appears to be a helpful treatment for controlling tooth decay." The results also showed that using chewing gum with a sorbitol-aspartame-saccharin sweetening mixture and not chewing any gum was ineffective in maintaining suppression of the tooth-decaying bacteria.
American Dental Association, ADA Web site at www.ada.orq., 2001
Text II. Fluorine and teeth
The peculiar relationship between fluorine and calcium must be understood in order to recognize the importance of fluorine in relation to the teeth.
Fluorine is the most negative element to be found. It has more combining property than oxygen. Death occurs by precipitating the whole blood calcium. If we realize how oxygen combines with iron, making it rust and how it combines with hemoglobin, making life possible, we will realize what it means to say that the combining property of fluorine is greater then that of oxygen. It has a tremendous attraction for calcium. All the fluorine taken into the circulation of the body from the drinking water is attracted by the calcium of the bones and teeth.
It is known also that normal enamel contains fluorine. Since nature seldom creates the superfluous, it has been suggested and commonly accepted that fluorine helps to make the structure of enamel stronger. It has been reported that the use of fluorine drinking water during calcification of the teeth resulted in a noticeable increase in resistance of the teeth to dental caries. This increased resistance was remarkably greater in cases where the people continued to use the fluorine drinking water permanently.
This observation indicates two different aspects of resistance of fluorine teeth to dental caries. One is present at the time of eruption, the other acts after eruption. The one present at eruption is the layer of transparent enamel that is formed during calcification of the enamel matrix. Transparent enamel forms a barrier against invasion of microorganisms along the prism sheaths.