在MPEG系列标准中，______最适合在共用电话交换网(PSTN)上实时传输视频数

书架平均每层放20本书，每个书架有四层，照这样计算，30个书架放多少本书？

光电二极管加<（）>电压能产生电流，发光二极管<（）>电压下工作。

A、反向偏置，正向偏置

B、正向偏置，反向偏置

C、正向偏置，正向偏置

D、反向偏置，反向偏置

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

信用卡的功能不包括( )。

A．投资

B．消费信用

C．转账结算

D．提取现金

筒形球磨煤机内堵煤时，入口负压变正，出口温度下降，压差增大，滚筒入口向外冒煤粉，筒体声音沉闷。