治疗阵发性睡眠性血红蛋白尿病，红细胞输注采用去除血浆并经盐水洗涤的次数为（）
A.3次
B.5次
C.4次
D.6次
E.2次
参考答案：A
I have been living in the United States for 20 years, but seldom ______ so lonely as now.
A．have I felt
B．I had felt
C．I have felt
D．had I felt
立式金刚石镗床开动时，（）变换手柄位臵。
A.可以
B.不可
C.迅速
D.立即
