[单项选择]癞皮病主要是由于______缺乏引起的。
A. 维生素B₁
B. 维生素B₂
C. 维生素B₆
D. 烟酸
E. 维生素C

The Great Wall of China
Walls and wall building have played a very important role in Chinese culture. These people, from the dim mists of prehistory have been wail-conscious; from the Neolithic period when ramparts of pounded earth were used to the Communist Revolution, walls were an essential part of any village. Not only towns and villages; the houses and the temples within them were somehow walled, and the houses also had no windows overlooking the street, thus giving the feeling of wandering around a huge maze. The name for "city" in Chinese (cheng) means wall, and over these walled cities, villages, houses and temples presides the god of walls and mounts, whose duties were, and still are, to protect and be responsible for the welfare of the inhabitants. Thus a great and extremely laborious task such as constructing a wall, which was supposed to-run throughout the country, must not have seemed such an absurdity.
However, it is indeed a common
A. was built in a single dynasty
B. was refurbished in the fourth and third centuries BC
C. used existing foundations
D. was built by the Chin, the Chao and the Yen

"We want Singapore to have the X-factor, that buzz that you get in London, Paris, or New York." That is how Lee Hsien Loong, Singapore’s prime minister, (1) his government’s decision to (2) gambling in the country, (3) two large, Vegas-style casinos. Whether the casinos will indeed help to transform Singapore’s staid image remains to be seen. But the decision bas already (4) an uncharacteristic buzz among the country’s normally (5) citizens.
The government has contemplated, and rejected (6) casinos several times in the past. One reason was (7) Singapore’s economic growth was so rapid that casinos seemed like an unnecessary evil. Buddhism and Islam, two of the country’s main religions, (8) on gambling. The government itself has traditionally had strong, and often (9) , ideas about how its citizens should behave. Until recently, for example, it refused to (10) A. in the name of
B. in the form o{
C. by the means of
D. in the need of