边长为a的正方体八个顶点上各有一电荷为q的点电荷，它们在上面中心O形成的合场强大
题型：问答题
问题：
边长为a的正方体八个顶点上各有一电荷为q的点电荷，它们在上面中心O形成的合场强大小是（ ）
A．0
B．8
kq6 9a2
C．
kq6 9a2
D．8kq 9a2 
题型：问答题
以下是几个国际节日的简要介绍：
A．Wharfedale Festival of Performing Arts West Yorkshire, the United Kingdom
Young people are invited to compete in this art festival with classes covering speech, guitar, dance, poetry and short story writing, and so on. The previous year's winners are invited back to perform again at a special concert. With a long and well-known history behind it, this well-attended competition is a kind of forerunner of popular television talent contests such as Pop Idol.
B．Sydney Writers' Festival Sydney, Australia
Held at Sydney's Wharf 4/5, the annual Sydney Writers' Festival is the biggest literary event of its kind in Australia and one of the biggest book fairs in t
he world. Attracting a mix of authors, poets, editors, publishers and book lovers, this is a great event at which people can look through thousands of titles while enjoying workshops, book reading and seminars.
C．Flipside Festival Singapore
As part of the Singapore Arts Festival Outreach Programme, Flipside aims to reach a much wider audience with three weeks of lively, fun street performances. Flipside promises to bring out the adventurous side of you with a combination of physical theatre and mind games as well as free outdoor performances such as music performances from local singers.
D．Hay Festival Hay on Wye, the United Kingdom
The little market town, Hay, has a population of 1500 and no fewer than 39 bookshops. It bills itself as the world's first and most distinguished book town, and is, therefore, a perfect place for
a literary festival. The festival is a celebration of great writing. There are events including film screenings and musical concerts and the bookshops remain open throughout.
E. Bergen International Festival Bergen, Norway
Founded in 1953, the Bergen International Festival presents an impressive cast of outstanding international artists in the fields of music, ballet, opera and other performing arts. More than 120 events take place in late May to early June, which is a time of beautiful spring weather. The main festival venue is the Grieg Hall while the smallest and most unusual is an old trolley bus with seating for just 33 people.
F. Nuits Sonores Lyon, France
Held each May, this relatively new festival brings together some of the biggest club DJs from around the world. The focus is on electronic dance music, but it also embraces all musical forms ranging from hip hop to jazz. For those that want to see daylight hours after a hard night clubbing, there is a wide variety of cultural events during the day ranging from special festival food programmes to films.
