People who work rotating night shifts appear to have a lower (47) of Parkinson’s disease, the results of a study published in the American Journal of Epidemiology. And (48) , an increased risk of developing this condition is linked to a longer average duration of sleep.
"Working rotating night shifts disrupts rhythms and may have a wide (49) of physiologic (理疗) effects on shift workers," Dr. Honglei Chen, of the National Institutes of Health, writes.
"In the (50) studies, some inference has been confirmed. Shift work has been (51) to higher risks of some chronic diseases, including certain types of cancers," they note, but any effect on the risk of developing Parkinson’s disease has not been (52) .
The researchers therefore (53) data from the U.S. Nurses’ Health Study, which enrolled 84, 794 female nurses, to see if there was an association between working rotating night shifts and Parkinson’s disease risk. The risk of Parkinson’s disease was 50-percent lower among women who had at least 15 years of night shift work compared with those who never worked rotating night shifts.
After (54) for differences in age and smoking status, the investigators found that a longer sleep duration was associated with a higher risk of Parkinson’s disease.
Plausible explanations for these results are lacking, Chen’s team points out. They note that shift
work has been associated with (55) increase in blood level of uric acid (尿酸), "which may be (56) against Parkinson’s disease."

• A) thereforeI) doubtful
• B) previousJ) number
• C) range K) little
• D) linked L) later
• E) risk M) modest
• F) investigated N) protective
• G) conversely O) evaluated
• H) accounting

某食品公司生产袋装饼干，其容量服从正态分布，已知标准差σ＝3g，标准规定每袋容量为245g。

假定袋装饼干的均值95%置信区间长度不超过2.1g，则样本容量至少为（）。

A．32

B．31

C．5

D．6