问题 选择题

面包里的孔洞是什么原因所致(  )

A.蒸气

B.加碱

C.二氧化碳受热膨胀

D.酵母菌解体

答案

做馒头或面包时,经常要用到酵母菌,酵母菌可以分解面粉中的葡萄糖,产生二氧化碳,二氧化碳是气体,遇热膨胀而形成小孔,使得馒头或面包暄软多空.可见C符合题意.

故选:C

问答题 简答题
单项选择题

This week marks the 10th anniversary of the Alar apple scare, in which many American consumers were driven into a panic following the release of a report by an environmental organization claiming that apples containing the chemical Alar posed a serious health threat to preschoolers. The report was disseminated through a PR (Problem Report) campaign and bypassed any legitimate form of scientific peer review. Introduced to the American public by CBS "60 Minutes", the unsubstantiated claims in the report led some school districts to remove apples from their school lunch programs and unduly frightened conscientious parents trying to develop good eating habits for their children.

Last month, Consumers Union released a report warning consumers of the perils of consuming many fruits and vegetables that frequently contained "unsafe" levels of pesticide residues. This was especially true for children, they claimed. Like its predecessor 10 years earlier, the Consumers Union report received no legitimate scientific peer review and the public’s first exposure to it was through news coverage.

Not only does such reporting potentially drive children for consuming healthful fruits and vegetables, the conclusions were based on a misleading interpretation of what constitutes a "safe" level of exposure. Briefly, the authors used values known as the "chronic reference doses", set by the U. S. environmental Protection Agency, as their barometers of safely. Used appropriately, these levels represent the maximum amount of pesticide that could be consumed daily for life without concern. For a 70-year lifetime, for example, consumers would have to ingest this average amount of pesticide every day for more than 25,000 days. It is clear, as the report points out, that there are days on which kids may be exposed to more; it is also clear that there are many more days when exposure is zero. Had the authors more appropriately calculated the cumulative exposures for which the safety standards are meant to apply, there would have been no risks and no warnings.

Parents should feel proud, rather than guilty, of providing fruits and vegetables for their children. It is well established that a diet rich in such foods decreases the risk of heart disease and cancer. Such benefits dramatically overwhelm the theoretical risks of tiny amounts of pesticides in food. So keep serving up the peaches, apples, squash, grapes and pears.

In the Mar apple scare, many Americans were frightened because ().

A. scientists warned that apples were dangerous

B. many school children became ill after eating apples

C. it was reported that apples were harmful to health

D. apples were discovered to have too much pesticide