引起先天性水疝的病因是（）
A.脾虚生湿
B.寒湿外侵
C.水窦不行
D.肾阳不足
E.膀胱气化无力
参考答案：C
假设普通音频电话线路支持的频率范围为300～3300Hz，信噪比为30dB，则该线路的带宽B是 (17) Hz，根据信息论原理，工作在该线路上的调制解调器最高速率C约为 (18) Kbps。
A．300 B．600 C．3000 D．3300
Which of the following statements is true of futures contracts()
A. All futures contracts are bought and sold on organized exchanges and the terms of futures contracts are determined by the buyers and sellers themselves.
B. The Clearinghouse serves to guarantee the performance of all parties to futures contracts.
C. Both are true.
