慢性阻塞性肺气肿的主要症状为（）
A.心悸
B.口唇发绀
C.右心衰竭
D.突发性喘息
E.逐渐加重的呼吸困难
参考答案：E
-- I could hardly understand what the foreigner said just now.
-- ______, even though I have learned English for two years.[ ]
A. So could I
B. Neither could I
C. So couldn't I
D. Hardly could I
曲线道岔类型有（）。
A、对称三开曲线道岔
B、两侧曲线道岔
C、同侧双边曲线道岔
D、单开曲线道岔
