本初子午线是

    There once was a man who played the piano in a bar. He was a good pianist People went there just to hear him play.But one night,a customer____told him he didn't want to hear him just play any more.He was____to sing a song by the customer.

    “I don't sing,”the man said.The customer said to the boss;“I'm____of just listening to the piano .I want that guy to sing!”

    “Hey,buddy!”the boss ____across the room.“If you want to get paid,sing a song!The customer is asking you to sing!” And the other customers were ____to see what would happen.

    So he did.He sang a song.A____who never sang in public did so for the very first time. What's more,Nat King Cloe sang the song,Mona Lisa,in a very special way.That was the ____time the song ever sounded that.

    He was so talented!He could have lived the rest of his life as a no-name piano player in a no-name bar.But because that man made ____sing,he went on to become one of the best-known ____in America.

You,too,have talent and abilities.You may not feel as if your talent is great,but it may be ____than you think!

下图为某种类型的板块边界示意图，图示板块边界处出现了(    )

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。