21. At one time doctors discouraged taking multivitamins because they believed that multivitamins ____.

　　A) could not easily be absorbed by the human body

　　B) were potentially harmful to people's health

　　C) were too expensive for daily consumption

　　D) could not provide any cure for vitamin deficiencies

　　22. According to the author, clinical trials of vitamin supplements ____.

　　A) often result in misleading conclusions

　　B) take time and will not produce conclusive results

　　C) should be conducted by scientists on a larger scale

　　D) appear to be a sheer waste of time and resources

　　23. It has been found that vitamin E _____.

　　A) should be taken by patients regularly and persistently

　　B) can effectively reduce the recurrence of heart disease

　　C) has a preventive but not curative effect on heart disease

　　D) should be given to patients with heart disease as early as possible

　　24. It can be seen that large doses of multivitamins _____.

　　A) may bring about serious side effects

　　B) may help prevent excessive bleeding

　　C) are likely to induce the blockage of arteries

　　D) are advisable for those with vitamin deficiencies

　　25. The author concludes the passage with the advice that _____.

　　A) the benefit of daily multivitamin intake outweighs that of exercise and a balanced diet

　　B) it's risky to take multivitamins without knowing their specific function

　　C) the potential benefit of multivitamins can never be overestimated

　　D) it's reasonable to take a rational dose of multivitamins daily