Canada and the United States are two immigrant countries, and more than 80% of them are white immigrants from European countries. 7 ~ 10 was completed according to the data and drawings. The following

Canada and the United States are two immigrant countries, and more than 80% of them are white immigrants from European countries. 7 ~ 10 was completed according to the data and drawings. The following questions are about addition. Canadian and American residents are mainly composed of immigrants and their descendants who moved in in different historical periods, and they are countries with complex races and nationalities;

Europeans arrived in north America after crossing the Atlantic, so a is correct;

Asians crossed the Pacific Ocean and Bering Strait to reach North America, so B was wrong;

Black Africans arrived in North America as slaves, not voluntarily, so C is wrong;

It is easier to travel between Africa and North America through the Atlantic Ocean, so D is wrong.

So choose: a.