问题
选择题
将正方形ABCD沿对角线BD折成一个120°的二面角，点C到达点C1，这时异面直线AD与BC1所成的角的余弦值是
( )
A. B.
C. D.
答案
答案：D
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将正方形ABCD沿对角线BD折成一个120°的二面角，点C到达点C1，这时异面直线AD与BC1所成的角的余弦值是
( )
A. B.
C. D.
答案：D
Most American families like to have a holiday in summer. Summer is a good season _36_ holidays. It is very _37_ during the months of July and August. Children do not go to school during these _38 months. Some _39_ like to stay at home during the holiday. They work in the garden, _40_ friends, _41_ books, or watch TV. Many families _42_ their lunch to a park or somewhere far from the city. They like to eat where there are many trees or there is a nice lake. _43_they live near the sea, they often go to the beach. They can fish, swim or enjoy the sun there. America is a large country. Many families travel by_44_ or by train to see interesting places. They also travel by plane to a foreign （外国的）country. Many big cities have many famous buildings, theatres, shops and _45_places for travellers (旅行者).
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