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

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．

试题答案

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