Question

课文填空

　　Exactly when the first people arrived in 　　1　　 as California, no one really knows．

　　Scientists believe that these first setters crossed the Berlin Strait from Asia to Alaska 　　2　　 of a land bridge．

　　Thousands were killed or 　　3　　 slavery．　　4　　, many 　　5　　 brought by Europeans．

　　Cloning has two 　　6　　．Firstly,…Secondly, it is valuable for research on 　　7　　 and for medical research on animals．…Many 　　8　　 to clone mammals failed．But at last the 　　9　　 of the scientists was rewarded in 1996 　　10　　－the cloning of Dolly the sheep．

Answer 1

答案：
解析：

　　1．what we now know

　　2．by means of

　　3．forced into

　　4．In addition

　　5．died from

　　6．major uses

　　7．new plant species

　　8．attempts

　　9．determination and patience

　　10．with a breakthrough