多克隆免疫球蛋白增高的常见原因不包括（）
A.慢性感染
B.肉芽肿病
C.多发性骨髓瘤
D.自身免疫性疾病
E.淋巴组织增殖性疾病
参考答案：C
Old people must _____.[ ]
A. be spoken to politely
B. speak to polite
C. be spoken politely
D. speak polite
Edward, you play so well. But I _____ you played the piano. [ ]
A. didn't know
B. hadn't known
C. don't know
D. haven't known
