A:美国以南的美洲国家和地区
B:墨西哥以南的美洲地区
C:巴拿马运河以南的美洲地区
D:整个南美洲
阅读下列短文,根据短文内容选择最佳答案.
Interesting festivals in the world
Throwing tomatoes﹣Spain(西班牙)
Spain takes "tomatoes fights" to a whole new level. But the tomatoes are being thrown, not eaten. The festival takes place during the last Wednesday in August. Trucks(卡车)carry tomatoes into the square. People rush to the tomatoes and throw them into the crowd.
Rolling cheese﹣England
This festival is celebrated on the last Monday in May. It takes place on Cooper's Hill. A large wheel of cheese(奶酪)is rolled down Cooper's Hill. The festival is actually a race where people run down the hill after the rolling cheese. The first person to cross the finish line at the bottom of the hill wins the cheese.
Burning man﹣The United States
The Burning Man Festival lasts a week, it is from the Monday before labor Day to Labor Day(which falls on the first Monday in September in America). The festival takes place in the Black Rock Desert. The best part of the festival is the burning of a large sculpture of a man.
Pouring water﹣Thailand
The Songkran Festival is the celebration of the New Year in Thailand. Rather than a single day. Thailand celebrates the New Year from April 13th to April 15th. Thai people run after each other pouring water. Songkran is one of the most important reasons why foreigners travel to the beautiful land.
下列材料为人类染色体数目确定的科学历程:
①20世纪初,细胞学家提出人体细胞染色体数目为47条,其中一条为“副”染色体,即现知的X染色体。
②1923年科学家又发现了仅存在于男性细胞中的Y染色体,得出了人体细胞共有48条染色体的结论,并分别用“46+XX”和“46+XY”表示女性和男性体细胞中染色体的组成。
③1955年科学家最终确定了人类染色体的正确数目,即人体细胞共有46条(23对)染色体,其中包括两条性染色体:女性为XX,男性为XY。