音位是一个语音系统中_______的最小语音单位。
参考答案：能够区别意义
用治血不养心引起的虚烦不眠、惊悸怔忡之证，宜选用的药物是（）
A.酸枣仁、柏子仁
B.石菖蒲、远志
C.合欢皮、龙骨
D.朱砂、磁石
E.珍珠母、琥珀
Someone called me at midnight, but he hung up _____ I could answer it. [ ]
A. as
B. since
C. after
D. before
