在计算机网络中，实现数字信号和模拟信号之间转换的设备是______。
参考答案：调制解调器
解析：在计算机网络中，调制解调器进行数字信号和模拟信号之间的转换。
如图所示，线框ABCD从有界的匀强磁场区域穿过，下列说法中正确的是（ ）
A．进入匀强磁场区域的过程中，ABCD中有感应电流
B．在匀强磁场中加速运动时，ABCD中有感应电流
C．在匀强磁场中匀速运动时，ABCD中有感应电流
D．离开匀强磁场区域的过程中，ABCD中没有感应电流
An investor is considering the purchase of two bonds. One of the bonds is tax-exempt and yields 4.5% while the other bond is taxable and yield 6.0%. If the two bonds are alike in all other characteristics, the rate that would make the investor indifferent between the two bonds is closest to:（）
A. 9.0%.
B. 25.0%.
C. 27.0%.
