A、A calm effect B、A shocking effect C、A fascinating effect D、A surprising effect A

The essential fact about smoking, which most commentators of recent years seem to have ignored, is that cigarettes give a vast number of people a good deal of pleasure. That is why the world smoked almost 5 trillion of them last year, approximately 1 200 for every man, woman and child on earth.
    It is not advertising that makes the Chinese smoke heavily any more than it was immoral merchants who persuaded the seventeenth century Persians to smoke, despite the Shah’s brilliant but cruel punishment of pouring molten lead down their throats when smokers were caught.
    There is considerable evidence, surprisingly little publicized by cigarette manufacturers, that smoking produces certain beneficial effects on human beings. Frankenhauser showed that smoking counteracts the decrease in efficiency that typically occurs in boring situations, and that smokers improved their performance in complex choice situations while smoking. There is a growing body of evidence that nicotine can produce a calm effect during high emotional and shock situation, while on the other hand stimulating concentration in tedious situations.
Questions 18 to 20 are based on the passage you have just heard.
18. What’s the essential fact about smoking that most commentators of recent years seem to have ignored?
19. How did Shah of the seventeenth century Persia punish smokers?
20. What beneficial effects does smoking produce on human beings?