题目

Canada is a very large country. It is the second largest country in the world. By contrast it has a very small population. There are only about 29 million people there. Most Canadians are of British or French origin, and French is an official language of Canada as well as English. About 45% of the people are of British origin, that is, they or their parents or grandparents, etc., come from Britain. Nearly 30% are of French origin. Most of the French-Canadians live in the province ofQuebec. Over the years, people have come to live in Canada from many countries in the world. They are fr如图甲所示是水流形成图，我们对电流的成因（如图乙所示）的认识是通过分析图甲中水流 的成因来了解的，这种方法在物理学中称为        [     ]   A．比较法              B．类比法             C．等效法            D．控制变量法