C

    Pliny the Elder (老普林尼) wrote the first encyclopaedia with the help of his nephew. This work was made up of 37 books and had many subjects such as anthropology(人类学) and painting. Through the following few centuries, encyclopaedias were connected to religion (宗教). The first Christian edition appeared in 560 AD, and the first Muslim volume came to light soon after.

    One of the longest encyclopaedias ever was produced in 1403 when The Yongle Encyclopaedia《永乐大典》appeared in China. It had 11,095 volumes. Most of the original work has been lost .through the centuries, and people can see less than 400 volumes today. The word "encyclopaedia" coming from Greek means "a general knowledge". It has been .in use for at least 500 years.

    In the 20th century, the Encyclopaedia Britannica became the most well known western work of this type. At the same time, topical encyclopaedias became the most popular, covering different topics. At the end of the century, many publishers began to publish them in digital formats such as Compact Discs (CDs) and Digital Versatile Discs (DVDs).

如图所示电路，平行板电容器的一个极板与滑动变阻器的滑动端P相连接．电子以速度v₀垂直于电场线方向射入并穿过平行板间的电场．在保证电子还能穿出平行板间电场的情况下，若使滑动变阻器的滑动端P上移，则关于电容器极板上所带电量q和电子穿越平行板所需的时间t的说法正确的是（ ）