根据如图回答，当两手自然下垂时①和②所处的状态是（　　）

A．①和②收缩

B．①和②都舒张

C．①收缩②舒张

D．①舒张②收缩

During recent years we have heard much about "race": how this race does certain things and that race believes certain things and so on. Yet, the (51) phenomenon of race consists of few surface indications.

We judge race usually from the coloring of the skin: a white race, a brown race, a yellow race and a black race. But (52) you were to remove the skin you could not tell anything about the race to which the individual belonged. There is nothing in physical structure, the brain or the internal organs to (53) a difference.

There are four types of blood. All types are found in every race, and no type is distinct to any race. Human brains are the (54) . No scientists could examine a brain and tell you the race to which the individual belonged. Brains will (55) in size, but this occurs within every race. (56) does size have anything to do with intelligence. The largest brain ever examined belonged to a person of weak (57) . On the other hand, some of our most distinguished people have had (58) brains.

Mental tests which are reasonably (59) show no differences in intelligence between races. High and low test results both can be recorded by different members of any race. (60) equal educational advantages, there will be no difference in average standings, either on account of race or geographical location.

60().

A.Provided 

B.Concerning 

C.Given 

D.Following