Most Brazilians get along well with each other, _________ they are from different races(种族), including Americans, European settlers, and Africans,.

A．although

B．as a result

C．since

D．unless

国家标准规定的表面粗糙度的评定参数中Ra代表（）。

A、微观不平度十点高度

B、轮廓最大高度

C、表面不平度

D、轮廓算术平均偏差