A survey suggests that the royal wedding of Prince William and Kate Middleton _____ a great boost for British economy because a large number of visitors are expected to go.

A．will be

B．has been

C．was

D．be

关于灰质在中枢神经系统中的位置，下列说法正确的包括（）。

A.脊髓的灰质在外周，白质在中间

B.脊髓的白质在外周，灰质在中间

C.大脑的灰质在外层，白质在内部

D.大脑的白质在外层，灰质在内部