18．_________a US visitor visa twice, the old couple finally gave up their hope of going to America to experience Thanksgiving Day.

A．Having been refused

B．Being refused

C．Having refused

D．To be refused

多发性骨髓瘤患者进行血清蛋白电泳时典型改变是（）

A.α1球蛋白增加

B.γ球蛋白增加

C.M蛋白增加

D.β球蛋白增加

E.α2球蛋白增加