如图，一束单色光射入一玻璃球体，入射角为60°．己知光线在玻璃球内经一次反射后，再次折射回到空气中时与入射光线平行．此玻璃的折射率为（ ）
A．2
B．1.5
C．3
D．2
作出光线在玻璃球体内光路图，A、C是折射点，B反射点，OD平行于入射光线，由几何知识得，∠AOD=∠COD=60°，则∠OAB=30°
即入射角r=30°，入射角i=60°
所以折射率为n=
=sini sinr 3
故选C
A) 根据所读内容，在文章后第62—71小题的空格里填入恰当的单词。每个空格只填1个单词。 Venice, a city in the northeast of Italy, is famous throughout the world for its buildings and romantic canals (运河). But in February every year, people come to Venice for another reason. The city carnival fills the place with excitement and fun. This year, the celebration runs from February 4 to 21. Colorful costumes have always played a very important role in the Venetian carnival. The carnival happens at the start of the Christian fasting (斋戒) period of Lent. It was traditionally a time to go a bit crazy with eating, drinking, dancing and dressing up before the fast began. People used masks to hide their social identity so that the nobility(贵族) would look no different from the commoners. Today the carnival is largely for the tourists. “Venetians don’t dress up for Carnival after the age of 10.” Giuseppina Giudice, who has lived in the city all her life, told the Guardian. “All we see of Carnival is a river of strangers who flow into town to feel ‘Venetian’. They fill it, buy a cheap mask and leave with nothing but photographs of St Mark’s Square.” Some locals want to bring back the original (最初的) feel of Carnival. In 2009, two social networking groups started organizing their own carnival. Visitors were invited. But there were no expensive tickets or fancy ball dresses---- just an old-fashioned Italian street party. “Tourists are welcome to our party ---- the more we can show them about the real Venice rather than the postcard Venice, the better,” Matteo Secchi, one of the organizers, told the Guardian.
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